From 5b687883b00a2d2d0252bc460a87c6e35f303612 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tim=20Z=C3=B6ller?= <tim.zoeller@lambdaschmiede.com>
Date: Mon, 15 Dec 2025 21:55:17 +0100
Subject: [PATCH] Better Federation Support

---
 FEDERATION_TESTING_GUIDE.md                   | 516 ++++++++++++++++++
 .../fitpub/config/SecurityConfig.java         |   1 +
 .../fitpub/controller/UserController.java     | 110 +++-
 .../model/activitypub/WebFingerLink.java      |  55 ++
 .../model/activitypub/WebFingerResource.java  |  60 ++
 .../fitpub/model/dto/TimelineActivityDTO.java |  46 ++
 .../fitpub/model/entity/RemoteActivity.java   | 188 +++++++
 .../fitpub/repository/FollowRepository.java   |  10 +
 .../repository/RemoteActivityRepository.java  | 111 ++++
 .../fitpub/service/FederationService.java     |  47 ++
 .../fitpub/service/InboxProcessor.java        | 369 ++++++++++++-
 .../fitpub/service/NotificationService.java   |  35 ++
 .../fitpub/service/TimelineService.java       | 163 +++++-
 .../fitpub/service/WebFingerClient.java       | 249 +++++++++
 .../V13__create_remote_activities_table.sql   |  63 +++
 src/main/resources/static/js/timeline.js      |  49 +-
 .../resources/templates/users/discover.html   | 205 ++++++-
 .../FederationFollowFlowIntegrationTest.java  | 418 ++++++++++++++
 .../service/TrainingLoadServiceTest.java      |  14 +-
 .../fitpub/service/WebFingerClientTest.java   | 217 ++++++++
 src/test/resources/application-test.yml       |  52 ++
 src/test/resources/init-test-db.sql           |   2 +
 22 files changed, 2931 insertions(+), 49 deletions(-)
 create mode 100644 FEDERATION_TESTING_GUIDE.md
 create mode 100644 src/main/java/org/operaton/fitpub/model/activitypub/WebFingerLink.java
 create mode 100644 src/main/java/org/operaton/fitpub/model/activitypub/WebFingerResource.java
 create mode 100644 src/main/java/org/operaton/fitpub/model/entity/RemoteActivity.java
 create mode 100644 src/main/java/org/operaton/fitpub/repository/RemoteActivityRepository.java
 create mode 100644 src/main/java/org/operaton/fitpub/service/WebFingerClient.java
 create mode 100644 src/main/resources/db/migration/V13__create_remote_activities_table.sql
 create mode 100644 src/test/java/org/operaton/fitpub/integration/FederationFollowFlowIntegrationTest.java
 create mode 100644 src/test/java/org/operaton/fitpub/service/WebFingerClientTest.java
 create mode 100644 src/test/resources/application-test.yml
 create mode 100644 src/test/resources/init-test-db.sql

diff --git a/FEDERATION_TESTING_GUIDE.md b/FEDERATION_TESTING_GUIDE.md
new file mode 100644
index 0000000..73edbe9
--- /dev/null
+++ b/FEDERATION_TESTING_GUIDE.md
@@ -0,0 +1,516 @@
+# FitPub Federation Testing Guide
+
+This guide explains how to test the instance-to-instance federation functionality by running two FitPub instances locally.
+
+## Prerequisites
+
+- Java 17+
+- Maven 3.8+
+- PostgreSQL 13+ with PostGIS extension
+- Two separate PostgreSQL databases
+- Two different port numbers for the applications
+
+## Setup
+
+### Step 1: Create Two PostgreSQL Databases
+
+```bash
+# Connect to PostgreSQL
+psql -U postgres
+
+# Create databases
+CREATE DATABASE fitpub_instance1;
+CREATE DATABASE fitpub_instance2;
+
+# Enable PostGIS extension for both databases
+\c fitpub_instance1
+CREATE EXTENSION IF NOT EXISTS postgis;
+
+\c fitpub_instance2
+CREATE EXTENSION IF NOT EXISTS postgis;
+
+\q
+```
+
+### Step 2: Prepare Application Profiles
+
+Create two separate application configuration files:
+
+#### `application-instance1.yml`
+
+```yaml
+server:
+  port: 8080
+
+spring:
+  datasource:
+    url: jdbc:postgresql://localhost:5432/fitpub_instance1
+    username: postgres
+    password: your_password
+  jpa:
+    hibernate:
+      ddl-auto: validate
+
+fitpub:
+  base-url: http://localhost:8080
+  domain: localhost:8080
+
+logging:
+  level:
+    org.operaton.fitpub: DEBUG
+```
+
+#### `application-instance2.yml`
+
+```yaml
+server:
+  port: 8081
+
+spring:
+  datasource:
+    url: jdbc:postgresql://localhost:5432/fitpub_instance2
+    username: postgres
+    password: your_password
+  jpa:
+    hibernate:
+      ddl-auto: validate
+
+fitpub:
+  base-url: http://localhost:8081
+  domain: localhost:8081
+
+logging:
+  level:
+    org.operaton.fitpub: DEBUG
+```
+
+### Step 3: Build the Application
+
+```bash
+mvn clean package -DskipTests
+```
+
+## Running the Instances
+
+### Terminal 1: Start Instance 1
+
+```bash
+java -jar target/feditrack-1.0-SNAPSHOT.jar --spring.profiles.active=instance1
+```
+
+Wait for the application to start completely. You should see:
+```
+Started FitPubApplication in X.XXX seconds
+```
+
+### Terminal 2: Start Instance 2
+
+```bash
+java -jar target/feditrack-1.0-SNAPSHOT.jar --spring.profiles.active=instance2
+```
+
+## Test Scenarios
+
+### Test 1: User Registration
+
+**Instance 1 (http://localhost:8080)**
+1. Navigate to http://localhost:8080/register
+2. Register user: `alice` / `alice@localhost1.test` / `password123`
+3. Login
+
+**Instance 2 (http://localhost:8081)**
+1. Navigate to http://localhost:8081/register
+2. Register user: `bob` / `bob@localhost2.test` / `password123`
+3. Login
+
+### Test 2: WebFinger Discovery
+
+**From Instance 1, discover Bob on Instance 2:**
+
+```bash
+curl http://localhost:8080/.well-known/webfinger?resource=acct:bob@localhost:8081
+```
+
+Expected response:
+```json
+{
+  "subject": "acct:bob@localhost:8081",
+  "aliases": [
+    "http://localhost:8081/users/bob"
+  ],
+  "links": [
+    {
+      "rel": "self",
+      "type": "application/activity+json",
+      "href": "http://localhost:8081/users/bob"
+    }
+  ]
+}
+```
+
+**From Instance 2, discover Alice on Instance 1:**
+
+```bash
+curl http://localhost:8081/.well-known/webfinger?resource=acct:alice@localhost:8080
+```
+
+### Test 3: Remote User Discovery via UI
+
+**On Instance 1 (Alice following Bob):**
+
+1. Login as Alice
+2. Navigate to http://localhost:8080/discover
+3. In the "Follow Remote Users" section, enter: `bob@localhost:8081`
+4. Click "Search"
+5. Verify Bob's profile appears with avatar, display name, and bio
+6. Click "Follow" button
+7. Verify notification appears: "Follow request sent to bob@localhost:8081"
+
+**Verify on Instance 2 (Bob's perspective):**
+
+1. Login as Bob on http://localhost:8081
+2. Check notifications - you should see: "alice@localhost:8080 followed you"
+3. Navigate to http://localhost:8081/users/bob/followers
+4. Verify alice@localhost:8080 appears in followers list
+
+### Test 4: Following Relationship Check
+
+**Check via API:**
+
+```bash
+# From Instance 2, check Bob's followers
+curl http://localhost:8081/api/users/bob/followers | jq
+
+# Expected: Alice should be in the list
+```
+
+**Check via UI:**
+
+On Instance 2:
+1. Navigate to http://localhost:8081/users/bob
+2. Check "Followers" count - should be 1
+3. Click on "Followers" - Alice should be listed
+
+On Instance 1:
+1. Navigate to http://localhost:8080/users/alice
+2. Check "Following" count - should be 1
+3. Click on "Following" - Bob should be listed
+
+### Test 5: Activity Federation
+
+**Bob uploads a workout on Instance 2:**
+
+1. Login as Bob on http://localhost:8081
+2. Navigate to http://localhost:8081/upload
+3. Upload a FIT file (use test file from `src/test/resources/`)
+4. Set title: "Morning 10K Run"
+5. Set visibility: "Public"
+6. Click "Upload"
+
+**Verify on Instance 1 (Alice's federated timeline):**
+
+1. Login as Alice on http://localhost:8080
+2. Navigate to http://localhost:8080/timeline/federated
+3. Verify Bob's "Morning 10K Run" activity appears with:
+   - Federation badge: "🌐 Remote"
+   - Bob's avatar and @bob@localhost:8081
+   - Map preview (if map image URL is available)
+   - Metrics (distance, duration, pace, elevation)
+   - Link to view on origin server
+
+### Test 6: Remote Activity Details
+
+**Click on Remote Activity:**
+
+From Alice's federated timeline:
+1. Click on Bob's "Morning 10K Run" activity title
+2. Verify it opens Bob's activity on Instance 2 (http://localhost:8081/activities/{id}) in a new tab
+3. Alternatively, click "View on Origin Server" button
+
+### Test 7: Incoming Activity via ActivityPub
+
+**Test with manual ActivityPub POST:**
+
+```bash
+# Create a test activity
+cat > test-activity.json <<EOF
+{
+  "@context": "https://www.w3.org/ns/activitystreams",
+  "type": "Create",
+  "id": "http://localhost:8081/activities/create/test-123",
+  "actor": "http://localhost:8081/users/bob",
+  "published": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
+  "to": ["https://www.w3.org/ns/activitystreams#Public"],
+  "cc": ["http://localhost:8081/users/bob/followers"],
+  "object": {
+    "type": "Note",
+    "id": "http://localhost:8081/workouts/test-456",
+    "attributedTo": "http://localhost:8081/users/bob",
+    "name": "Test Workout via ActivityPub",
+    "content": "Testing direct ActivityPub activity delivery",
+    "published": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
+    "to": ["https://www.w3.org/ns/activitystreams#Public"],
+    "workoutData": {
+      "activityType": "RUN",
+      "distance": 5000,
+      "duration": "PT25M30S",
+      "elevationGain": 50
+    },
+    "attachment": [
+      {
+        "type": "Document",
+        "mediaType": "image/png",
+        "name": "Map",
+        "url": "http://localhost:8081/activities/test-456/map.png"
+      }
+    ]
+  }
+}
+EOF
+
+# Post to Alice's inbox on Instance 1
+curl -X POST http://localhost:8080/users/alice/inbox \
+  -H "Content-Type: application/activity+json" \
+  -d @test-activity.json
+
+# Expected response: 202 Accepted
+```
+
+**Verify in database:**
+
+```sql
+-- On Instance 1
+SELECT * FROM remote_activities WHERE remote_actor_uri = 'http://localhost:8081/users/bob';
+```
+
+### Test 8: Unfollow Workflow
+
+**Alice unfollows Bob:**
+
+1. On Instance 1, navigate to http://localhost:8080/users/alice/following
+2. Find Bob in the following list
+3. Click "Unfollow"
+4. Verify confirmation dialog
+5. Confirm unfollow
+
+**Verify Undo Activity:**
+
+Check Instance 2 logs for incoming Undo activity:
+```
+Processing Undo activity for user bob
+Deleted follow from actor: http://localhost:8080/users/alice
+```
+
+**Check Database:**
+
+```sql
+-- On Instance 2
+SELECT * FROM follows WHERE remote_actor_uri = 'http://localhost:8080/users/alice'
+  AND following_actor_uri = 'http://localhost:8081/users/bob';
+-- Should return 0 rows
+```
+
+### Test 9: Accept Activity Flow
+
+**Bob follows Alice (reverse direction):**
+
+1. On Instance 2, login as Bob
+2. Navigate to http://localhost:8081/discover
+3. Search for: `alice@localhost:8080`
+4. Click "Follow"
+5. Verify "Follow request sent" notification
+
+**Check Follow Status:**
+
+```sql
+-- On Instance 2
+SELECT status FROM follows WHERE follower_id = (SELECT id FROM users WHERE username = 'bob')
+  AND following_actor_uri = 'http://localhost:8080/users/alice';
+-- Should return 'PENDING'
+```
+
+**Verify Accept on Instance 1:**
+
+Check Instance 1 logs for outgoing Accept activity:
+```
+Sending Accept activity to http://localhost:8081/users/bob/inbox
+Accept activity sent successfully
+```
+
+**Check Updated Status:**
+
+```sql
+-- On Instance 2
+SELECT status FROM follows WHERE follower_id = (SELECT id FROM users WHERE username = 'bob')
+  AND following_actor_uri = 'http://localhost:8080/users/alice';
+-- Should return 'ACCEPTED'
+```
+
+**Check Notification:**
+
+On Instance 2:
+1. Navigate to http://localhost:8081/notifications
+2. Verify notification: "alice@localhost:8080 accepted your follow request"
+
+## Troubleshooting
+
+### Instance Won't Start
+
+**Problem:** Port already in use
+```
+Port 8080 is already in use
+```
+
+**Solution:** Kill the process using the port or use a different port
+```bash
+lsof -ti:8080 | xargs kill -9
+```
+
+### Database Connection Error
+
+**Problem:** Connection refused to PostgreSQL
+
+**Solution:** Check PostgreSQL is running
+```bash
+brew services start postgresql
+# or
+sudo systemctl start postgresql
+```
+
+### WebFinger Not Working
+
+**Problem:** 404 when accessing /.well-known/webfinger
+
+**Solution:**
+1. Check if the controller is mapped correctly
+2. Verify Spring Security allows unauthenticated access to WebFinger endpoint
+3. Check logs for any errors
+
+### Remote Activities Not Appearing
+
+**Problem:** Bob's activities don't show up in Alice's federated timeline
+
+**Solution:**
+1. Verify follow relationship exists and status is ACCEPTED:
+   ```sql
+   SELECT * FROM follows WHERE follower_id = (SELECT id FROM users WHERE username = 'alice')
+     AND following_actor_uri LIKE '%bob%';
+   ```
+2. Check InboxProcessor logs for incoming Create activities
+3. Verify RemoteActivity was created:
+   ```sql
+   SELECT * FROM remote_activities;
+   ```
+4. Check TimelineService is fetching both local and remote activities
+
+### Map Preview Not Loading
+
+**Problem:** Remote activity map shows "Map not available"
+
+**Solution:**
+- Remote activities use `mapImageUrl` field which must be set when creating the activity
+- For testing, you may need to implement map image generation on the origin server
+- Check if the URL in `map_image_url` is accessible
+
+## Validation Checklist
+
+- [ ] Both instances start successfully on different ports
+- [ ] WebFinger discovery works in both directions
+- [ ] Remote user discovery UI works
+- [ ] Follow request is sent and creates PENDING follow
+- [ ] Accept activity is received and updates status to ACCEPTED
+- [ ] Follower/following lists show both local and remote users
+- [ ] Remote activities appear in federated timeline
+- [ ] Remote activities show federation badge
+- [ ] Map preview loads from remote server
+- [ ] "View on Origin Server" opens correct URL
+- [ ] Unfollow sends Undo activity and removes follow
+- [ ] Notifications are created for follow/accept events
+- [ ] No errors in console logs
+
+## Database Inspection Queries
+
+### Check All Follows
+
+```sql
+-- On any instance
+SELECT
+  f.id,
+  f.follower_id,
+  u.username as follower_username,
+  f.following_actor_uri,
+  f.remote_actor_uri,
+  f.status,
+  f.created_at
+FROM follows f
+LEFT JOIN users u ON f.follower_id = u.id
+ORDER BY f.created_at DESC;
+```
+
+### Check Remote Actors
+
+```sql
+SELECT
+  actor_uri,
+  username,
+  domain,
+  display_name,
+  last_fetched
+FROM remote_actors
+ORDER BY last_fetched DESC;
+```
+
+### Check Remote Activities
+
+```sql
+SELECT
+  id,
+  activity_uri,
+  remote_actor_uri,
+  activity_type,
+  title,
+  total_distance,
+  total_duration_seconds,
+  published_at,
+  visibility,
+  map_image_url
+FROM remote_activities
+ORDER BY published_at DESC;
+```
+
+## Clean Up
+
+To reset the test environment:
+
+```bash
+# Stop both instances (Ctrl+C in both terminals)
+
+# Drop and recreate databases
+psql -U postgres <<EOF
+DROP DATABASE fitpub_instance1;
+DROP DATABASE fitpub_instance2;
+CREATE DATABASE fitpub_instance1;
+CREATE DATABASE fitpub_instance2;
+\c fitpub_instance1
+CREATE EXTENSION IF NOT EXISTS postgis;
+\c fitpub_instance2
+CREATE EXTENSION IF NOT EXISTS postgis;
+EOF
+```
+
+## Additional Testing Tips
+
+1. **Use Browser Developer Tools** to inspect network requests for ActivityPub activities
+2. **Monitor Logs** in both terminal windows to see federation events in real-time
+3. **Test Edge Cases** like following yourself, duplicate follows, following non-existent users
+4. **Test Different Visibility Levels** (PUBLIC, FOLLOWERS, PRIVATE)
+5. **Simulate Network Failures** by stopping one instance mid-federation
+6. **Test Concurrent Operations** (both users following each other simultaneously)
+
+## Success Criteria
+
+✅ All checklist items pass
+✅ No errors in logs
+✅ Activities federate within 1-2 seconds
+✅ UI updates reflect federation state correctly
+✅ Database state is consistent across both instances
diff --git a/src/main/java/org/operaton/fitpub/config/SecurityConfig.java b/src/main/java/org/operaton/fitpub/config/SecurityConfig.java
index d60542c..0775b7e 100644
--- a/src/main/java/org/operaton/fitpub/config/SecurityConfig.java
+++ b/src/main/java/org/operaton/fitpub/config/SecurityConfig.java
@@ -121,6 +121,7 @@ public class SecurityConfig {
                 .requestMatchers(HttpMethod.GET, "/api/users/id/*").permitAll()
                 .requestMatchers(HttpMethod.GET, "/api/users/search").permitAll() // User search
                 .requestMatchers(HttpMethod.GET, "/api/users/browse").permitAll() // Browse all users
+                .requestMatchers(HttpMethod.GET, "/api/users/discover-remote").authenticated() // Remote user discovery
                 .requestMatchers(HttpMethod.GET, "/api/users/*/followers").permitAll() // User followers list
                 .requestMatchers(HttpMethod.GET, "/api/users/*/following").permitAll() // User following list
                 .requestMatchers(HttpMethod.GET, "/api/users/*/follow-status").permitAll() // Follow status check
diff --git a/src/main/java/org/operaton/fitpub/controller/UserController.java b/src/main/java/org/operaton/fitpub/controller/UserController.java
index 1d58591..71907f6 100644
--- a/src/main/java/org/operaton/fitpub/controller/UserController.java
+++ b/src/main/java/org/operaton/fitpub/controller/UserController.java
@@ -39,6 +39,8 @@ public class UserController {
     private final UserRepository userRepository;
     private final FollowRepository followRepository;
     private final RemoteActorRepository remoteActorRepository;
+    private final org.operaton.fitpub.service.WebFingerClient webFingerClient;
+    private final org.operaton.fitpub.service.FederationService federationService;
 
     @Value("${fitpub.base-url}")
     private String baseUrl;
@@ -198,6 +200,44 @@ public class UserController {
         return ResponseEntity.ok(userDTOs);
     }
 
+    /**
+     * Discover a remote user via WebFinger.
+     * Takes a handle in the format @username@domain or username@domain,
+     * performs WebFinger discovery, fetches the remote actor, and returns actor information.
+     *
+     * @param handle the handle of the remote user (@username@domain)
+     * @param userDetails the authenticated user making the request
+     * @return ActorDTO containing remote user information
+     */
+    @GetMapping("/discover-remote")
+    public ResponseEntity<ActorDTO> discoverRemoteUser(
+        @RequestParam String handle,
+        @AuthenticationPrincipal UserDetails userDetails
+    ) {
+        log.info("User {} discovering remote user: {}", userDetails.getUsername(), handle);
+
+        try {
+            // 1. WebFinger lookup to discover actor URI
+            String actorUri = webFingerClient.discoverActor(handle);
+            log.debug("Discovered actor URI: {}", actorUri);
+
+            // 2. Fetch remote actor information
+            RemoteActor remoteActor = federationService.fetchRemoteActor(actorUri);
+            log.debug("Fetched remote actor: {}", remoteActor.getUsername());
+
+            // 3. Convert to DTO and return (no follow relationship yet, so followedAt is null)
+            ActorDTO dto = ActorDTO.fromRemoteActor(remoteActor, null);
+            return ResponseEntity.ok(dto);
+
+        } catch (IllegalArgumentException e) {
+            log.error("Invalid handle format: {}", handle, e);
+            return ResponseEntity.badRequest().build();
+        } catch (Exception e) {
+            log.error("Error discovering remote user: {}", handle, e);
+            return ResponseEntity.status(500).build();
+        }
+    }
+
     /**
      * Get list of followers for a user.
      *
@@ -275,9 +315,9 @@ public class UserController {
     }
 
     /**
-     * Follow a user.
+     * Follow a user (local or remote).
      *
-     * @param username the username to follow
+     * @param username the username to follow (local username or @username@domain format)
      * @param userDetails the authenticated user
      * @return success response
      */
@@ -292,6 +332,22 @@ public class UserController {
         User currentUser = userRepository.findByUsername(userDetails.getUsername())
             .orElseThrow(() -> new UsernameNotFoundException("Current user not found"));
 
+        // Check if this is a remote user (contains @ and position > 0)
+        boolean isRemoteUser = username.contains("@") && username.indexOf("@") > 0;
+
+        if (isRemoteUser) {
+            // Remote user follow
+            return followRemoteUser(username, currentUser);
+        } else {
+            // Local user follow
+            return followLocalUser(username, currentUser);
+        }
+    }
+
+    /**
+     * Follow a local user (auto-accepted).
+     */
+    private ResponseEntity<Map<String, Object>> followLocalUser(String username, User currentUser) {
         // Get the user to follow
         User userToFollow = userRepository.findByUsername(username)
             .orElseThrow(() -> new UsernameNotFoundException("User not found: " + username));
@@ -342,6 +398,56 @@ public class UserController {
         ));
     }
 
+    /**
+     * Follow a remote user via ActivityPub (requires Accept from remote).
+     */
+    private ResponseEntity<Map<String, Object>> followRemoteUser(String handle, User currentUser) {
+        try {
+            log.info("Following remote user: {}", handle);
+
+            // 1. Discover remote actor using WebFinger
+            String remoteActorUri = webFingerClient.discoverActor(handle);
+            log.debug("Discovered remote actor URI: {}", remoteActorUri);
+
+            // 2. Check if already following
+            Optional<Follow> existingFollow = followRepository.findByFollowerIdAndFollowingActorUri(
+                currentUser.getId(), remoteActorUri
+            );
+
+            if (existingFollow.isPresent()) {
+                Follow follow = existingFollow.get();
+                if (follow.getStatus() == Follow.FollowStatus.ACCEPTED) {
+                    return ResponseEntity.badRequest()
+                        .body(Map.of("error", "Already following this user"));
+                } else {
+                    return ResponseEntity.ok(Map.of(
+                        "message", "Follow request already pending for " + handle,
+                        "status", "PENDING"
+                    ));
+                }
+            }
+
+            // 3. Send Follow activity to remote actor
+            // This will also create a PENDING follow record
+            federationService.sendFollowActivity(remoteActorUri, currentUser);
+
+            return ResponseEntity.ok(Map.of(
+                "message", "Follow request sent to " + handle,
+                "status", "PENDING",
+                "note", "Waiting for acceptance from remote user"
+            ));
+
+        } catch (IllegalArgumentException e) {
+            log.warn("Invalid handle format: {}", handle, e);
+            return ResponseEntity.badRequest()
+                .body(Map.of("error", "Invalid handle format: " + e.getMessage()));
+        } catch (Exception e) {
+            log.error("Failed to follow remote user: {}", handle, e);
+            return ResponseEntity.status(500)
+                .body(Map.of("error", "Failed to follow remote user: " + e.getMessage()));
+        }
+    }
+
     /**
      * Unfollow a user.
      *
diff --git a/src/main/java/org/operaton/fitpub/model/activitypub/WebFingerLink.java b/src/main/java/org/operaton/fitpub/model/activitypub/WebFingerLink.java
new file mode 100644
index 0000000..1be155c
--- /dev/null
+++ b/src/main/java/org/operaton/fitpub/model/activitypub/WebFingerLink.java
@@ -0,0 +1,55 @@
+package org.operaton.fitpub.model.activitypub;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+/**
+ * Represents a link in a WebFinger response (RFC 7033).
+ *
+ * Example:
+ * {
+ *   "rel": "self",
+ *   "type": "application/activity+json",
+ *   "href": "https://fitpub.example/users/username"
+ * }
+ */
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+@JsonInclude(JsonInclude.Include.NON_NULL)
+public class WebFingerLink {
+
+    /**
+     * The relationship type (e.g., "self", "http://webfinger.net/rel/profile-page").
+     */
+    private String rel;
+
+    /**
+     * The media type of the linked resource (e.g., "application/activity+json").
+     */
+    private String type;
+
+    /**
+     * The URL of the linked resource.
+     */
+    private String href;
+
+    /**
+     * Optional template for the link (used for some link types).
+     */
+    private String template;
+
+    /**
+     * Optional titles for the link in different languages.
+     */
+    private java.util.Map<String, String> titles;
+
+    /**
+     * Optional properties for the link.
+     */
+    private java.util.Map<String, String> properties;
+}
diff --git a/src/main/java/org/operaton/fitpub/model/activitypub/WebFingerResource.java b/src/main/java/org/operaton/fitpub/model/activitypub/WebFingerResource.java
new file mode 100644
index 0000000..17468cf
--- /dev/null
+++ b/src/main/java/org/operaton/fitpub/model/activitypub/WebFingerResource.java
@@ -0,0 +1,60 @@
+package org.operaton.fitpub.model.activitypub;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Represents a WebFinger resource response (RFC 7033).
+ *
+ * Example:
+ * {
+ *   "subject": "acct:username@domain.com",
+ *   "aliases": ["https://domain.com/users/username"],
+ *   "links": [
+ *     {
+ *       "rel": "self",
+ *       "type": "application/activity+json",
+ *       "href": "https://domain.com/users/username"
+ *     },
+ *     {
+ *       "rel": "http://webfinger.net/rel/profile-page",
+ *       "type": "text/html",
+ *       "href": "https://domain.com/@username"
+ *     }
+ *   ]
+ * }
+ */
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+@JsonInclude(JsonInclude.Include.NON_NULL)
+public class WebFingerResource {
+
+    /**
+     * The subject identifier (usually in acct: URI format).
+     * Example: "acct:username@domain.com"
+     */
+    private String subject;
+
+    /**
+     * Alternative URIs for the same resource.
+     */
+    private List<String> aliases;
+
+    /**
+     * Links to related resources.
+     */
+    private List<WebFingerLink> links;
+
+    /**
+     * Optional properties (key-value pairs).
+     */
+    private Map<String, String> properties;
+}
diff --git a/src/main/java/org/operaton/fitpub/model/dto/TimelineActivityDTO.java b/src/main/java/org/operaton/fitpub/model/dto/TimelineActivityDTO.java
index e8c282c..923639f 100644
--- a/src/main/java/org/operaton/fitpub/model/dto/TimelineActivityDTO.java
+++ b/src/main/java/org/operaton/fitpub/model/dto/TimelineActivityDTO.java
@@ -5,8 +5,11 @@ import lombok.Builder;
 import lombok.Data;
 import lombok.NoArgsConstructor;
 import org.operaton.fitpub.model.entity.Activity;
+import org.operaton.fitpub.model.entity.RemoteActivity;
+import org.operaton.fitpub.model.entity.RemoteActor;
 
 import java.time.LocalDateTime;
+import java.time.ZoneId;
 import java.util.UUID;
 
 /**
@@ -38,6 +41,10 @@ public class TimelineActivityDTO {
     private String avatarUrl;
     private boolean isLocal;
 
+    // Remote activity fields (only populated for federated activities)
+    private String activityUri;  // Full ActivityPub URI (for remote activities)
+    private String mapImageUrl;  // Map image URL (for remote activities)
+
     // Social interaction counts
     private Long likesCount;
     private Long commentsCount;
@@ -71,6 +78,45 @@ public class TimelineActivityDTO {
             .build();
     }
 
+    /**
+     * Convert RemoteActivity entity to timeline DTO.
+     * Used for displaying federated activities from other FitPub instances.
+     */
+    public static TimelineActivityDTO fromRemoteActivity(RemoteActivity remote, RemoteActor actor) {
+        // Create metrics summary from remote activity fields
+        ActivityMetricsSummary metrics = ActivityMetricsSummary.builder()
+            .averageHeartRate(remote.getAverageHeartRate())
+            .averageSpeed(remote.getAverageSpeed())
+            .maxSpeed(remote.getMaxSpeed())
+            .averagePaceSeconds(remote.getAveragePaceSeconds())
+            .calories(remote.getCalories())
+            .build();
+
+        return TimelineActivityDTO.builder()
+            .id(remote.getId())
+            .activityType(remote.getActivityType() != null ? remote.getActivityType() : "UNKNOWN")
+            .title(remote.getTitle())
+            .description(remote.getDescription())
+            .startedAt(remote.getPublishedAt() != null
+                ? LocalDateTime.ofInstant(remote.getPublishedAt(), ZoneId.systemDefault())
+                : null)
+            .endedAt(null) // Not available for remote activities
+            .totalDistance(remote.getTotalDistance() != null ? remote.getTotalDistance().doubleValue() : null)
+            .totalDurationSeconds(remote.getTotalDurationSeconds())
+            .elevationGain(remote.getElevationGain() != null ? remote.getElevationGain().doubleValue() : null)
+            .elevationLoss(null) // Not available for remote activities
+            .visibility(remote.getVisibility() != null ? remote.getVisibility().name() : "PUBLIC")
+            .createdAt(remote.getCreatedAt())
+            .username(actor.getUsername())
+            .displayName(actor.getDisplayName() != null ? actor.getDisplayName() : actor.getUsername())
+            .avatarUrl(actor.getAvatarUrl())
+            .isLocal(false)
+            .activityUri(remote.getActivityUri())
+            .mapImageUrl(remote.getMapImageUrl())
+            .metrics(metrics)
+            .build();
+    }
+
     /**
      * Summary of activity metrics for timeline display.
      */
diff --git a/src/main/java/org/operaton/fitpub/model/entity/RemoteActivity.java b/src/main/java/org/operaton/fitpub/model/entity/RemoteActivity.java
new file mode 100644
index 0000000..e91dc96
--- /dev/null
+++ b/src/main/java/org/operaton/fitpub/model/entity/RemoteActivity.java
@@ -0,0 +1,188 @@
+package org.operaton.fitpub.model.entity;
+
+import io.hypersistence.utils.hibernate.type.json.JsonBinaryType;
+import jakarta.persistence.*;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import org.hibernate.annotations.CreationTimestamp;
+import org.hibernate.annotations.Type;
+import org.hibernate.annotations.UpdateTimestamp;
+
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.util.UUID;
+
+/**
+ * Entity representing a remote fitness activity from another FitPub instance or ActivityPub server.
+ *
+ * IMPORTANT: This entity stores METADATA ONLY - no full track data.
+ * Track visualization is done via remote map image URLs pointing to the origin server.
+ */
+@Entity
+@Table(name = "remote_activities", indexes = {
+    @Index(name = "idx_remote_activity_uri", columnList = "activity_uri", unique = true),
+    @Index(name = "idx_remote_activity_actor", columnList = "remote_actor_uri"),
+    @Index(name = "idx_remote_activity_published", columnList = "published_at"),
+    @Index(name = "idx_remote_activity_visibility", columnList = "visibility")
+})
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class RemoteActivity {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private UUID id;
+
+    /**
+     * ActivityPub activity URI (globally unique identifier).
+     * Example: https://fitpub.example/activities/12345
+     */
+    @Column(name = "activity_uri", nullable = false, unique = true, length = 512)
+    private String activityUri;
+
+    /**
+     * ActivityPub actor URI of the user who created this activity.
+     * Example: https://fitpub.example/users/alice
+     */
+    @Column(name = "remote_actor_uri", nullable = false, length = 512)
+    private String remoteActorUri;
+
+    /**
+     * Type of activity (RUN, RIDE, HIKE, SWIM, etc.).
+     */
+    @Column(name = "activity_type", length = 50)
+    private String activityType;
+
+    /**
+     * Activity title.
+     */
+    @Column(name = "title", nullable = false, length = 500)
+    private String title;
+
+    /**
+     * Activity description/notes.
+     */
+    @Column(name = "description", columnDefinition = "TEXT")
+    private String description;
+
+    /**
+     * When the activity was published (from ActivityPub).
+     */
+    @Column(name = "published_at", nullable = false)
+    private Instant publishedAt;
+
+    /**
+     * Total distance in meters.
+     */
+    @Column(name = "total_distance")
+    private Long totalDistance;
+
+    /**
+     * Total duration in seconds.
+     */
+    @Column(name = "total_duration_seconds")
+    private Long totalDurationSeconds;
+
+    /**
+     * Total elevation gain in meters.
+     */
+    @Column(name = "elevation_gain")
+    private Integer elevationGain;
+
+    /**
+     * Average pace in seconds per kilometer (for runs).
+     */
+    @Column(name = "average_pace_seconds")
+    private Long averagePaceSeconds;
+
+    /**
+     * Average heart rate in BPM.
+     */
+    @Column(name = "average_heart_rate")
+    private Integer averageHeartRate;
+
+    /**
+     * Maximum speed in km/h.
+     */
+    @Column(name = "max_speed")
+    private Double maxSpeed;
+
+    /**
+     * Average speed in km/h.
+     */
+    @Column(name = "average_speed")
+    private Double averageSpeed;
+
+    /**
+     * Calories burned (if provided).
+     */
+    @Column(name = "calories")
+    private Integer calories;
+
+    /**
+     * URL to the map image on the remote server.
+     * This points to a static map image generated by the origin server.
+     */
+    @Column(name = "map_image_url", length = 512)
+    private String mapImageUrl;
+
+    /**
+     * URL to the GeoJSON track data on the remote server (optional).
+     * If provided, allows dynamic map rendering.
+     */
+    @Column(name = "track_geojson_url", length = 512)
+    private String trackGeojsonUrl;
+
+    /**
+     * Visibility level of the activity.
+     */
+    @Enumerated(EnumType.STRING)
+    @Column(name = "visibility", nullable = false, length = 20)
+    private Visibility visibility;
+
+    /**
+     * Full ActivityPub object as JSON (for future re-parsing or debugging).
+     * Stored as JSONB for efficient querying.
+     */
+    @Type(JsonBinaryType.class)
+    @Column(name = "activitypub_object", columnDefinition = "jsonb")
+    private String activityPubObject;
+
+    /**
+     * Timestamp when this record was created locally.
+     */
+    @CreationTimestamp
+    @Column(name = "created_at", nullable = false, updatable = false)
+    private LocalDateTime createdAt;
+
+    /**
+     * Timestamp when this record was last updated.
+     */
+    @UpdateTimestamp
+    @Column(name = "updated_at")
+    private LocalDateTime updatedAt;
+
+    /**
+     * Visibility levels for remote activities.
+     */
+    public enum Visibility {
+        /**
+         * Public activity visible to everyone.
+         */
+        PUBLIC,
+
+        /**
+         * Activity visible only to followers.
+         */
+        FOLLOWERS,
+
+        /**
+         * Private activity (should not be federated, but included for completeness).
+         */
+        PRIVATE
+    }
+}
diff --git a/src/main/java/org/operaton/fitpub/repository/FollowRepository.java b/src/main/java/org/operaton/fitpub/repository/FollowRepository.java
index 774dacc..31c00d3 100644
--- a/src/main/java/org/operaton/fitpub/repository/FollowRepository.java
+++ b/src/main/java/org/operaton/fitpub/repository/FollowRepository.java
@@ -67,4 +67,14 @@ public interface FollowRepository extends JpaRepository<Follow, UUID> {
      * @return the follow relationship if it exists
      */
     Optional<Follow> findByActivityId(String activityId);
+
+    /**
+     * Find a follow relationship by remote actor URI and following actor URI.
+     * Used to check if a remote user is following a local user.
+     *
+     * @param remoteActorUri the remote actor's URI (follower)
+     * @param followingActorUri the actor URI being followed
+     * @return the follow relationship if it exists
+     */
+    Optional<Follow> findByRemoteActorUriAndFollowingActorUri(String remoteActorUri, String followingActorUri);
 }
diff --git a/src/main/java/org/operaton/fitpub/repository/RemoteActivityRepository.java b/src/main/java/org/operaton/fitpub/repository/RemoteActivityRepository.java
new file mode 100644
index 0000000..b9656a7
--- /dev/null
+++ b/src/main/java/org/operaton/fitpub/repository/RemoteActivityRepository.java
@@ -0,0 +1,111 @@
+package org.operaton.fitpub.repository;
+
+import org.operaton.fitpub.model.entity.RemoteActivity;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.UUID;
+
+/**
+ * Repository for RemoteActivity entity.
+ * Provides methods for querying remote fitness activities from federated instances.
+ */
+@Repository
+public interface RemoteActivityRepository extends JpaRepository<RemoteActivity, UUID> {
+
+    /**
+     * Finds a remote activity by its ActivityPub URI.
+     * Used for deduplication and activity lookup.
+     *
+     * @param activityUri the ActivityPub activity URI
+     * @return optional remote activity
+     */
+    Optional<RemoteActivity> findByActivityUri(String activityUri);
+
+    /**
+     * Checks if a remote activity exists by its ActivityPub URI.
+     * Used for deduplication before storing.
+     *
+     * @param activityUri the ActivityPub activity URI
+     * @return true if exists
+     */
+    boolean existsByActivityUri(String activityUri);
+
+    /**
+     * Finds remote activities by a specific remote actor.
+     *
+     * @param remoteActorUri the remote actor URI
+     * @param pageable pagination parameters
+     * @return page of remote activities
+     */
+    Page<RemoteActivity> findByRemoteActorUri(String remoteActorUri, Pageable pageable);
+
+    /**
+     * Finds remote activities from multiple actors with specific visibility levels.
+     * Used for federated timeline - shows activities from users you follow.
+     *
+     * @param actorUris list of remote actor URIs
+     * @param visibilities list of allowed visibility levels (PUBLIC, FOLLOWERS)
+     * @param pageable pagination parameters
+     * @return page of remote activities
+     */
+    @Query("SELECT ra FROM RemoteActivity ra WHERE ra.remoteActorUri IN :actorUris " +
+           "AND ra.visibility IN :visibilities " +
+           "ORDER BY ra.publishedAt DESC")
+    Page<RemoteActivity> findByRemoteActorUriInAndVisibilityIn(
+        @Param("actorUris") List<String> actorUris,
+        @Param("visibilities") List<RemoteActivity.Visibility> visibilities,
+        Pageable pageable
+    );
+
+    /**
+     * Finds all public remote activities.
+     * Used for public timeline.
+     *
+     * @param pageable pagination parameters
+     * @return page of public remote activities
+     */
+    @Query("SELECT ra FROM RemoteActivity ra WHERE ra.visibility = 'PUBLIC' " +
+           "ORDER BY ra.publishedAt DESC")
+    Page<RemoteActivity> findAllPublicActivities(Pageable pageable);
+
+    /**
+     * Counts remote activities from a specific actor.
+     *
+     * @param remoteActorUri the remote actor URI
+     * @return count of activities
+     */
+    long countByRemoteActorUri(String remoteActorUri);
+
+    /**
+     * Finds activities by type from specific actors.
+     * Used for filtering by activity type.
+     *
+     * @param actorUris list of remote actor URIs
+     * @param activityType the activity type (RUN, RIDE, etc.)
+     * @param pageable pagination parameters
+     * @return page of activities
+     */
+    @Query("SELECT ra FROM RemoteActivity ra WHERE ra.remoteActorUri IN :actorUris " +
+           "AND ra.activityType = :activityType " +
+           "ORDER BY ra.publishedAt DESC")
+    Page<RemoteActivity> findByRemoteActorUriInAndActivityType(
+        @Param("actorUris") List<String> actorUris,
+        @Param("activityType") String activityType,
+        Pageable pageable
+    );
+
+    /**
+     * Deletes all remote activities from a specific actor.
+     * Used when unfollowing or blocking a remote user.
+     *
+     * @param remoteActorUri the remote actor URI
+     */
+    void deleteByRemoteActorUri(String remoteActorUri);
+}
diff --git a/src/main/java/org/operaton/fitpub/service/FederationService.java b/src/main/java/org/operaton/fitpub/service/FederationService.java
index 3f997f4..9735608 100644
--- a/src/main/java/org/operaton/fitpub/service/FederationService.java
+++ b/src/main/java/org/operaton/fitpub/service/FederationService.java
@@ -119,6 +119,53 @@ public class FederationService {
         }
     }
 
+    /**
+     * Send a Follow activity to a remote actor.
+     *
+     * @param remoteActorUri the URI of the remote actor to follow
+     * @param localUser the local user initiating the follow
+     */
+    @Transactional
+    public void sendFollowActivity(String remoteActorUri, User localUser) {
+        try {
+            log.info("Sending Follow activity from {} to {}", localUser.getUsername(), remoteActorUri);
+
+            // 1. Fetch remote actor to get inbox URL and cache their info
+            RemoteActor remoteActor = fetchRemoteActor(remoteActorUri);
+
+            // 2. Create Follow activity
+            String followId = baseUrl + "/activities/follow/" + UUID.randomUUID();
+            String actorUri = baseUrl + "/users/" + localUser.getUsername();
+
+            Map<String, Object> followActivity = new HashMap<>();
+            followActivity.put("@context", "https://www.w3.org/ns/activitystreams");
+            followActivity.put("type", "Follow");
+            followActivity.put("id", followId);
+            followActivity.put("actor", actorUri);
+            followActivity.put("object", remoteActorUri);
+            followActivity.put("published", Instant.now().toString());
+
+            // 3. Send to remote actor's inbox (HTTP-signed)
+            sendActivity(remoteActor.getInboxUrl(), followActivity, localUser);
+
+            // 4. Create local follow record with PENDING status
+            // The status will be updated to ACCEPTED when we receive an Accept activity
+            Follow follow = Follow.builder()
+                .followerId(localUser.getId())
+                .followingActorUri(remoteActorUri)
+                .status(Follow.FollowStatus.PENDING)
+                .activityId(followId)
+                .build();
+            followRepository.save(follow);
+
+            log.info("Follow activity sent successfully: {} -> {}", localUser.getUsername(), remoteActorUri);
+
+        } catch (Exception e) {
+            log.error("Failed to send Follow activity from {} to {}", localUser.getUsername(), remoteActorUri, e);
+            throw new RuntimeException("Failed to send Follow activity", e);
+        }
+    }
+
     /**
      * Send an Accept activity in response to a Follow.
      *
diff --git a/src/main/java/org/operaton/fitpub/service/InboxProcessor.java b/src/main/java/org/operaton/fitpub/service/InboxProcessor.java
index 5deccf0..3dae22d 100644
--- a/src/main/java/org/operaton/fitpub/service/InboxProcessor.java
+++ b/src/main/java/org/operaton/fitpub/service/InboxProcessor.java
@@ -17,6 +17,7 @@ import org.springframework.beans.factory.annotation.Value;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
+import java.time.Instant;
 import java.util.Map;
 import java.util.UUID;
 
@@ -35,6 +36,8 @@ public class InboxProcessor {
     private final LikeRepository likeRepository;
     private final CommentRepository commentRepository;
     private final NotificationService notificationService;
+    private final org.operaton.fitpub.repository.RemoteActivityRepository remoteActivityRepository;
+    private final org.operaton.fitpub.repository.RemoteActorRepository remoteActorRepository;
 
     @Value("${fitpub.base-url}")
     private String baseUrl;
@@ -166,16 +169,40 @@ public class InboxProcessor {
     private void processAccept(String username, Map<String, Object> activity) {
         try {
             Object object = activity.get("object");
+            String activityId = null;
+
+            // Handle both embedded object (Map) and reference (String)
             if (object instanceof Map) {
                 @SuppressWarnings("unchecked")
                 Map<String, Object> acceptObject = (Map<String, Object>) object;
-                String activityId = (String) acceptObject.get("id");
+                activityId = (String) acceptObject.get("id");
+            } else if (object instanceof String) {
+                activityId = (String) object;
+            }
 
+            if (activityId != null) {
                 Follow follow = followRepository.findByActivityId(activityId).orElse(null);
                 if (follow != null && follow.getStatus() == Follow.FollowStatus.PENDING) {
+                    // Update follow status to ACCEPTED
                     follow.setStatus(Follow.FollowStatus.ACCEPTED);
                     followRepository.save(follow);
                     log.info("Follow request accepted: {}", activityId);
+
+                    // Create notification for the follower
+                    // The follower is the local user who initiated the follow request
+                    UUID followerId = follow.getFollowerId();
+                    if (followerId != null) {
+                        User follower = userRepository.findById(followerId).orElse(null);
+                        if (follower != null) {
+                            String remoteActorUri = follow.getFollowingActorUri();
+                            notificationService.createFollowAcceptedNotification(
+                                follower.getId(),
+                                remoteActorUri,
+                                activityId
+                            );
+                            log.info("Created follow accepted notification for user {}", follower.getUsername());
+                        }
+                    }
                 }
             }
         } catch (Exception e) {
@@ -206,11 +233,24 @@ public class InboxProcessor {
             }
 
             String inReplyTo = (String) noteObject.get("inReplyTo");
-            if (inReplyTo == null) {
-                log.debug("Create/Note is not a reply, ignoring");
-                return;
-            }
 
+            if (inReplyTo == null) {
+                // Standalone Note activity - could be a remote workout/activity
+                processRemoteActivity(username, actor, noteObject);
+            } else {
+                // Note with inReplyTo - this is a comment
+                processComment(username, actor, noteObject, inReplyTo);
+            }
+        } catch (Exception e) {
+            log.error("Error processing Create activity", e);
+        }
+    }
+
+    /**
+     * Process a comment (Note with inReplyTo).
+     */
+    private void processComment(String username, String actor, Map<String, Object> noteObject, String inReplyTo) {
+        try {
             // Extract activity ID from inReplyTo URI
             UUID activityId = extractActivityIdFromUri(inReplyTo);
             if (activityId == null) {
@@ -260,7 +300,82 @@ public class InboxProcessor {
             notificationService.createActivityCommentedNotification(localActivity, comment, actor);
 
         } catch (Exception e) {
-            log.error("Error processing Create activity", e);
+            log.error("Error processing comment", e);
+        }
+    }
+
+    /**
+     * Process a remote activity (standalone Note representing a workout/fitness activity).
+     */
+    private void processRemoteActivity(String username, String actor, Map<String, Object> noteObject) {
+        try {
+            String activityUri = (String) noteObject.get("id");
+            if (activityUri == null) {
+                log.warn("Remote activity has no id");
+                return;
+            }
+
+            // Check if activity already exists (deduplication)
+            if (remoteActivityRepository.existsByActivityUri(activityUri)) {
+                log.debug("Remote activity already exists: {}", activityUri);
+                return;
+            }
+
+            // Fetch and cache remote actor
+            RemoteActor remoteActor = federationService.fetchRemoteActor(actor);
+
+            // Check if local user follows this remote actor
+            User localUser = userRepository.findByUsername(username).orElse(null);
+            if (localUser == null) {
+                log.warn("Local user not found: {}", username);
+                return;
+            }
+
+            boolean isFollowing = followRepository.findByFollowerIdAndFollowingActorUri(
+                localUser.getId(), actor
+            ).map(follow -> follow.getStatus() == Follow.FollowStatus.ACCEPTED).orElse(false);
+
+            if (!isFollowing) {
+                log.debug("Local user {} is not following {}, ignoring activity", username, actor);
+                return;
+            }
+
+            // Extract workout metadata
+            Map<String, Object> workoutData = extractWorkoutData(noteObject);
+            Map<String, String> attachments = extractAttachments(noteObject);
+            org.operaton.fitpub.model.entity.RemoteActivity.Visibility visibility = determineVisibility(noteObject);
+
+            // Parse published timestamp
+            String publishedStr = (String) noteObject.get("published");
+            Instant publishedAt = publishedStr != null ? Instant.parse(publishedStr) : Instant.now();
+
+            // Build RemoteActivity entity
+            org.operaton.fitpub.model.entity.RemoteActivity remoteActivity = org.operaton.fitpub.model.entity.RemoteActivity.builder()
+                .activityUri(activityUri)
+                .remoteActorUri(actor)
+                .activityType((String) workoutData.get("activityType"))
+                .title((String) noteObject.getOrDefault("name", noteObject.getOrDefault("summary", "Untitled Activity")))
+                .description(stripHtml((String) noteObject.get("content")))
+                .publishedAt(publishedAt)
+                .totalDistance(parseLong(workoutData.get("distance")))
+                .totalDurationSeconds(parseDurationSeconds((String) workoutData.get("duration")))
+                .elevationGain(parseInteger(workoutData.get("elevationGain")))
+                .averagePaceSeconds(parseDurationSeconds((String) workoutData.get("averagePace")))
+                .averageHeartRate(parseInteger(workoutData.get("averageHeartRate")))
+                .maxSpeed(parseDouble(workoutData.get("maxSpeed")))
+                .averageSpeed(parseDouble(workoutData.get("averageSpeed")))
+                .calories(parseInteger(workoutData.get("calories")))
+                .mapImageUrl(attachments.get("mapImage"))
+                .trackGeojsonUrl(attachments.get("trackGeojson"))
+                .visibility(visibility)
+                .activityPubObject(serializeToJson(noteObject))
+                .build();
+
+            remoteActivityRepository.save(remoteActivity);
+            log.info("Stored remote activity from {}: {} ({})", remoteActor.getUsername(), remoteActivity.getTitle(), activityUri);
+
+        } catch (Exception e) {
+            log.error("Error processing remote activity", e);
         }
     }
 
@@ -360,4 +475,246 @@ public class InboxProcessor {
 
         return text.trim();
     }
+
+    // ==================== Remote Activity Helper Methods ====================
+
+    /**
+     * Extract workout/fitness data from a Note object.
+     * Looks for a "workoutData" extension field containing structured fitness metrics.
+     */
+    private Map<String, Object> extractWorkoutData(Map<String, Object> noteObject) {
+        Map<String, Object> workoutData = new java.util.HashMap<>();
+
+        // Check for custom workoutData extension (FitPub-specific)
+        Object workoutDataObj = noteObject.get("workoutData");
+        if (workoutDataObj instanceof Map) {
+            @SuppressWarnings("unchecked")
+            Map<String, Object> data = (Map<String, Object>) workoutDataObj;
+            workoutData.putAll(data);
+        }
+
+        // Fallback: Try to extract from summary or content
+        String summary = (String) noteObject.get("summary");
+        if (summary != null) {
+            // Parse summary like "10.2 km • 48:23 • 4:44/km pace"
+            workoutData.putIfAbsent("activityType", guessActivityType(summary));
+        }
+
+        return workoutData;
+    }
+
+    /**
+     * Extract attachment URLs (map image, GeoJSON) from a Note object.
+     */
+    private Map<String, String> extractAttachments(Map<String, Object> noteObject) {
+        Map<String, String> attachments = new java.util.HashMap<>();
+
+        Object attachmentObj = noteObject.get("attachment");
+        if (attachmentObj instanceof java.util.List) {
+            @SuppressWarnings("unchecked")
+            java.util.List<Object> attachmentList = (java.util.List<Object>) attachmentObj;
+
+            for (Object item : attachmentList) {
+                if (item instanceof Map) {
+                    @SuppressWarnings("unchecked")
+                    Map<String, Object> attach = (Map<String, Object>) item;
+
+                    String type = (String) attach.get("type");
+                    String mediaType = (String) attach.get("mediaType");
+                    String url = (String) attach.get("url");
+                    String name = (String) attach.get("name");
+
+                    if (url != null) {
+                        // Map image
+                        if ("Image".equals(type) && (mediaType != null && mediaType.startsWith("image/"))) {
+                            if (name != null && name.toLowerCase().contains("map")) {
+                                attachments.put("mapImage", url);
+                            }
+                        }
+                        // GeoJSON track
+                        else if ("Document".equals(type) && "application/geo+json".equals(mediaType)) {
+                            attachments.put("trackGeojson", url);
+                        }
+                    }
+                }
+            }
+        }
+
+        return attachments;
+    }
+
+    /**
+     * Determine visibility from ActivityPub "to" and "cc" fields.
+     */
+    private org.operaton.fitpub.model.entity.RemoteActivity.Visibility determineVisibility(Map<String, Object> noteObject) {
+        Object toObj = noteObject.get("to");
+        Object ccObj = noteObject.get("cc");
+
+        java.util.List<String> toList = objectToStringList(toObj);
+        java.util.List<String> ccList = objectToStringList(ccObj);
+
+        // Check if Public is in "to" or "cc"
+        boolean isPublic = toList.contains("https://www.w3.org/ns/activitystreams#Public") ||
+                          ccList.contains("https://www.w3.org/ns/activitystreams#Public") ||
+                          toList.contains("as:Public") ||
+                          ccList.contains("as:Public") ||
+                          toList.contains("Public") ||
+                          ccList.contains("Public");
+
+        if (isPublic) {
+            return org.operaton.fitpub.model.entity.RemoteActivity.Visibility.PUBLIC;
+        }
+
+        // If it has followers in to/cc, it's FOLLOWERS visibility
+        boolean hasFollowers = toList.stream().anyMatch(s -> s.contains("/followers")) ||
+                              ccList.stream().anyMatch(s -> s.contains("/followers"));
+
+        if (hasFollowers) {
+            return org.operaton.fitpub.model.entity.RemoteActivity.Visibility.FOLLOWERS;
+        }
+
+        // Default to PRIVATE
+        return org.operaton.fitpub.model.entity.RemoteActivity.Visibility.PRIVATE;
+    }
+
+    /**
+     * Parse ISO 8601 duration string (PT48M23S) to seconds.
+     */
+    private Long parseDurationSeconds(String isoDuration) {
+        if (isoDuration == null || isoDuration.isBlank()) {
+            return null;
+        }
+
+        try {
+            // Simple ISO 8601 duration parser for PT format
+            // Format: PT<hours>H<minutes>M<seconds>S
+            if (!isoDuration.startsWith("PT")) {
+                return null;
+            }
+
+            String duration = isoDuration.substring(2); // Remove "PT"
+            long totalSeconds = 0;
+
+            // Parse hours
+            if (duration.contains("H")) {
+                int hIndex = duration.indexOf("H");
+                totalSeconds += Long.parseLong(duration.substring(0, hIndex)) * 3600;
+                duration = duration.substring(hIndex + 1);
+            }
+
+            // Parse minutes
+            if (duration.contains("M")) {
+                int mIndex = duration.indexOf("M");
+                totalSeconds += Long.parseLong(duration.substring(0, mIndex)) * 60;
+                duration = duration.substring(mIndex + 1);
+            }
+
+            // Parse seconds
+            if (duration.contains("S")) {
+                int sIndex = duration.indexOf("S");
+                totalSeconds += Long.parseLong(duration.substring(0, sIndex));
+            }
+
+            return totalSeconds;
+        } catch (Exception e) {
+            log.warn("Failed to parse ISO duration: {}", isoDuration, e);
+            return null;
+        }
+    }
+
+    /**
+     * Serialize object to JSON string.
+     */
+    private String serializeToJson(Object object) {
+        try {
+            return new com.fasterxml.jackson.databind.ObjectMapper().writeValueAsString(object);
+        } catch (Exception e) {
+            log.error("Failed to serialize object to JSON", e);
+            return null;
+        }
+    }
+
+    /**
+     * Convert object to list of strings (handles both single string and list).
+     */
+    private java.util.List<String> objectToStringList(Object obj) {
+        if (obj == null) {
+            return java.util.Collections.emptyList();
+        }
+        if (obj instanceof String) {
+            return java.util.Collections.singletonList((String) obj);
+        }
+        if (obj instanceof java.util.List) {
+            @SuppressWarnings("unchecked")
+            java.util.List<Object> list = (java.util.List<Object>) obj;
+            return list.stream()
+                .filter(item -> item instanceof String)
+                .map(item -> (String) item)
+                .collect(java.util.stream.Collectors.toList());
+        }
+        return java.util.Collections.emptyList();
+    }
+
+    /**
+     * Guess activity type from text.
+     */
+    private String guessActivityType(String text) {
+        if (text == null) {
+            return "UNKNOWN";
+        }
+        String lower = text.toLowerCase();
+        if (lower.contains("run") || lower.contains("jog")) return "RUN";
+        if (lower.contains("ride") || lower.contains("bike") || lower.contains("cycl")) return "RIDE";
+        if (lower.contains("hike") || lower.contains("walk")) return "HIKE";
+        if (lower.contains("swim")) return "SWIM";
+        return "UNKNOWN";
+    }
+
+    /**
+     * Parse Long from object.
+     */
+    private Long parseLong(Object obj) {
+        if (obj == null) return null;
+        if (obj instanceof Number) return ((Number) obj).longValue();
+        if (obj instanceof String) {
+            try {
+                return Long.parseLong((String) obj);
+            } catch (NumberFormatException e) {
+                return null;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Parse Integer from object.
+     */
+    private Integer parseInteger(Object obj) {
+        if (obj == null) return null;
+        if (obj instanceof Number) return ((Number) obj).intValue();
+        if (obj instanceof String) {
+            try {
+                return Integer.parseInt((String) obj);
+            } catch (NumberFormatException e) {
+                return null;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Parse Double from object.
+     */
+    private Double parseDouble(Object obj) {
+        if (obj == null) return null;
+        if (obj instanceof Number) return ((Number) obj).doubleValue();
+        if (obj instanceof String) {
+            try {
+                return Double.parseDouble((String) obj);
+            } catch (NumberFormatException e) {
+                return null;
+            }
+        }
+        return null;
+    }
 }
diff --git a/src/main/java/org/operaton/fitpub/service/NotificationService.java b/src/main/java/org/operaton/fitpub/service/NotificationService.java
index 76fc516..aa77be2 100644
--- a/src/main/java/org/operaton/fitpub/service/NotificationService.java
+++ b/src/main/java/org/operaton/fitpub/service/NotificationService.java
@@ -155,6 +155,41 @@ public class NotificationService {
         log.debug("Created USER_FOLLOWED notification for user {} from {}", followedUser.getUsername(), actorInfo.username);
     }
 
+    /**
+     * Create a notification when a remote user accepts your follow request.
+     *
+     * @param followerId the ID of the user who initiated the follow
+     * @param acceptedActorUri the URI of the remote actor who accepted
+     * @param activityId the ActivityPub activity ID
+     */
+    public void createFollowAcceptedNotification(UUID followerId, String acceptedActorUri, String activityId) {
+        // Get follower user
+        User follower = userRepository.findById(followerId).orElse(null);
+        if (follower == null) {
+            log.warn("Could not find follower user with ID: {}", followerId);
+            return;
+        }
+
+        // Get actor information
+        ActorInfo actorInfo = getActorInfo(acceptedActorUri);
+        if (actorInfo == null) {
+            log.warn("Could not find actor info for URI: {}", acceptedActorUri);
+            return;
+        }
+
+        Notification notification = Notification.builder()
+            .user(follower)
+            .type(Notification.NotificationType.FOLLOW_ACCEPTED)
+            .actorUri(acceptedActorUri)
+            .actorDisplayName(actorInfo.displayName)
+            .actorUsername(actorInfo.username)
+            .actorAvatarUrl(actorInfo.avatarUrl)
+            .build();
+
+        notificationRepository.save(notification);
+        log.debug("Created FOLLOW_ACCEPTED notification for user {} from {}", follower.getUsername(), actorInfo.username);
+    }
+
     /**
      * Get all notifications for a user.
      *
diff --git a/src/main/java/org/operaton/fitpub/service/TimelineService.java b/src/main/java/org/operaton/fitpub/service/TimelineService.java
index 2575dac..3d94728 100644
--- a/src/main/java/org/operaton/fitpub/service/TimelineService.java
+++ b/src/main/java/org/operaton/fitpub/service/TimelineService.java
@@ -5,21 +5,28 @@ import lombok.extern.slf4j.Slf4j;
 import org.operaton.fitpub.model.dto.TimelineActivityDTO;
 import org.operaton.fitpub.model.entity.Activity;
 import org.operaton.fitpub.model.entity.Follow;
+import org.operaton.fitpub.model.entity.RemoteActivity;
+import org.operaton.fitpub.model.entity.RemoteActor;
 import org.operaton.fitpub.model.entity.User;
 import org.operaton.fitpub.repository.ActivityRepository;
 import org.operaton.fitpub.repository.FollowRepository;
+import org.operaton.fitpub.repository.RemoteActivityRepository;
+import org.operaton.fitpub.repository.RemoteActorRepository;
 import org.operaton.fitpub.repository.UserRepository;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageImpl;
+import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
 import java.util.ArrayList;
+import java.util.Comparator;
 import java.util.List;
 import java.util.UUID;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * Service for managing timelines.
@@ -33,6 +40,8 @@ public class TimelineService {
     private final ActivityRepository activityRepository;
     private final FollowRepository followRepository;
     private final UserRepository userRepository;
+    private final RemoteActivityRepository remoteActivityRepository;
+    private final RemoteActorRepository remoteActorRepository;
     private final org.operaton.fitpub.repository.LikeRepository likeRepository;
     private final org.operaton.fitpub.repository.CommentRepository commentRepository;
 
@@ -43,7 +52,8 @@ public class TimelineService {
      * Get the federated timeline for a user.
      * Includes public activities from:
      * - The user's own activities
-     * - Activities from users they follow (local users only for now)
+     * - Activities from local users they follow
+     * - Activities from remote users they follow (federated)
      *
      * @param userId the authenticated user's ID
      * @param pageable pagination parameters
@@ -56,44 +66,57 @@ public class TimelineService {
         User currentUser = userRepository.findById(userId)
             .orElseThrow(() -> new IllegalArgumentException("User not found: " + userId));
 
-        // Get list of user IDs that the current user follows
+        // 1. Get followed remote actor URIs
+        List<String> remoteActorUris = getFollowedRemoteActorUris(userId);
+
+        // 2. Get followed local user IDs
         List<UUID> followedUserIds = getFollowedLocalUserIds(userId);
+        followedUserIds.add(userId); // Include the current user's own activities
 
-        // Include the current user's own activities
-        followedUserIds.add(userId);
-
-        // Fetch public and followers-only activities from followed users
-        Page<Activity> activities = activityRepository.findByUserIdInAndVisibilityInOrderByStartedAtDesc(
+        // 3. Fetch local activities from followed users (fetch more to account for merging)
+        // We fetch double the page size to have enough items after merging
+        Pageable expandedPageable = PageRequest.of(0, pageable.getPageSize() * 2);
+        Page<Activity> localActivities = activityRepository.findByUserIdInAndVisibilityInOrderByStartedAtDesc(
             followedUserIds,
             List.of(Activity.Visibility.PUBLIC, Activity.Visibility.FOLLOWERS),
-            pageable
+            expandedPageable
         );
 
-        // Convert to DTOs
-        List<TimelineActivityDTO> timelineActivities = activities.getContent().stream()
-            .map(activity -> {
-                User activityUser = userRepository.findById(activity.getUserId()).orElse(null);
-                if (activityUser == null) {
-                    return null;
-                }
-                TimelineActivityDTO dto = TimelineActivityDTO.fromActivity(
-                    activity,
-                    activityUser.getUsername(),
-                    activityUser.getDisplayName() != null ? activityUser.getDisplayName() : activityUser.getUsername(),
-                    activityUser.getAvatarUrl()
-                );
+        // 4. Fetch remote activities from followed remote actors (if any)
+        List<RemoteActivity> remoteActivities = new ArrayList<>();
+        if (!remoteActorUris.isEmpty()) {
+            Page<RemoteActivity> remoteActivitiesPage = remoteActivityRepository.findByRemoteActorUriInAndVisibilityIn(
+                remoteActorUris,
+                List.of(RemoteActivity.Visibility.PUBLIC, RemoteActivity.Visibility.FOLLOWERS),
+                expandedPageable
+            );
+            remoteActivities = remoteActivitiesPage.getContent();
+        }
 
-                // Add social interaction counts
-                dto.setLikesCount(likeRepository.countByActivityId(activity.getId()));
-                dto.setCommentsCount(commentRepository.countByActivityIdAndNotDeleted(activity.getId()));
-                dto.setLikedByCurrentUser(likeRepository.existsByActivityIdAndUserId(activity.getId(), userId));
+        // 5. Merge local and remote activities
+        List<TimelineActivityDTO> mergedActivities = mergeActivities(
+            localActivities.getContent(),
+            remoteActivities,
+            userId
+        );
 
-                return dto;
-            })
-            .filter(dto -> dto != null)
-            .collect(Collectors.toList());
+        // 6. Sort chronologically (most recent first) and paginate
+        mergedActivities.sort((a, b) -> {
+            if (a.getStartedAt() == null && b.getStartedAt() == null) return 0;
+            if (a.getStartedAt() == null) return 1;
+            if (b.getStartedAt() == null) return -1;
+            return b.getStartedAt().compareTo(a.getStartedAt());
+        });
 
-        return new PageImpl<>(timelineActivities, pageable, activities.getTotalElements());
+        // Apply pagination to the merged list
+        int start = (int) pageable.getOffset();
+        int end = Math.min(start + pageable.getPageSize(), mergedActivities.size());
+        List<TimelineActivityDTO> paginatedActivities = mergedActivities.subList(
+            Math.min(start, mergedActivities.size()),
+            end
+        );
+
+        return new PageImpl<>(paginatedActivities, pageable, mergedActivities.size());
     }
 
     /**
@@ -205,4 +228,84 @@ public class TimelineService {
 
         return followedUserIds;
     }
+
+    /**
+     * Get actor URIs of remote users that the given user follows.
+     *
+     * @param userId the user's ID
+     * @return list of followed remote actor URIs
+     */
+    private List<String> getFollowedRemoteActorUris(UUID userId) {
+        List<Follow> follows = followRepository.findAcceptedFollowingByUserId(userId);
+        List<String> remoteActorUris = new ArrayList<>();
+
+        for (Follow follow : follows) {
+            // Check if the followed actor is a remote user (not on this instance)
+            String actorUri = follow.getFollowingActorUri();
+            if (!actorUri.startsWith(baseUrl + "/users/")) {
+                remoteActorUris.add(actorUri);
+            }
+        }
+
+        return remoteActorUris;
+    }
+
+    /**
+     * Merge local and remote activities into a single list of timeline DTOs.
+     *
+     * @param localActivities list of local Activity entities
+     * @param remoteActivities list of remote RemoteActivity entities
+     * @param currentUserId the current user's ID (for like status)
+     * @return merged list of TimelineActivityDTOs
+     */
+    private List<TimelineActivityDTO> mergeActivities(
+        List<Activity> localActivities,
+        List<RemoteActivity> remoteActivities,
+        UUID currentUserId
+    ) {
+        List<TimelineActivityDTO> merged = new ArrayList<>();
+
+        // Convert local activities to DTOs
+        for (Activity activity : localActivities) {
+            User activityUser = userRepository.findById(activity.getUserId()).orElse(null);
+            if (activityUser == null) {
+                continue;
+            }
+
+            TimelineActivityDTO dto = TimelineActivityDTO.fromActivity(
+                activity,
+                activityUser.getUsername(),
+                activityUser.getDisplayName() != null ? activityUser.getDisplayName() : activityUser.getUsername(),
+                activityUser.getAvatarUrl()
+            );
+
+            // Add social interaction counts
+            dto.setLikesCount(likeRepository.countByActivityId(activity.getId()));
+            dto.setCommentsCount(commentRepository.countByActivityIdAndNotDeleted(activity.getId()));
+            dto.setLikedByCurrentUser(likeRepository.existsByActivityIdAndUserId(activity.getId(), currentUserId));
+
+            merged.add(dto);
+        }
+
+        // Convert remote activities to DTOs
+        for (RemoteActivity remoteActivity : remoteActivities) {
+            RemoteActor actor = remoteActorRepository.findByActorUri(remoteActivity.getRemoteActorUri()).orElse(null);
+            if (actor == null) {
+                log.warn("Remote actor not found for URI: {}", remoteActivity.getRemoteActorUri());
+                continue;
+            }
+
+            TimelineActivityDTO dto = TimelineActivityDTO.fromRemoteActivity(remoteActivity, actor);
+
+            // Remote activities don't have like/comment counts in this implementation
+            // (would require additional federation support)
+            dto.setLikesCount(0L);
+            dto.setCommentsCount(0L);
+            dto.setLikedByCurrentUser(false);
+
+            merged.add(dto);
+        }
+
+        return merged;
+    }
 }
diff --git a/src/main/java/org/operaton/fitpub/service/WebFingerClient.java b/src/main/java/org/operaton/fitpub/service/WebFingerClient.java
new file mode 100644
index 0000000..1ab2a24
--- /dev/null
+++ b/src/main/java/org/operaton/fitpub/service/WebFingerClient.java
@@ -0,0 +1,249 @@
+package org.operaton.fitpub.service;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.URI;
+import java.net.UnknownHostException;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * WebFinger client for discovering ActivityPub actors on remote instances.
+ * Implements RFC 7033 WebFinger protocol with SSRF protection.
+ */
+@Service
+@RequiredArgsConstructor
+@Slf4j
+public class WebFingerClient {
+
+    private final ObjectMapper objectMapper;
+
+    @Value("${fitpub.domain}")
+    private String localDomain;
+
+    private static final int TIMEOUT_SECONDS = 5;
+    private static final String WEBFINGER_PATH = "/.well-known/webfinger";
+    private static final String ACTIVITYPUB_CONTENT_TYPE = "application/activity+json";
+
+    /**
+     * Discovers an ActivityPub actor URI from a handle.
+     *
+     * @param handle the handle in format @username@domain or username@domain
+     * @return the actor URI (e.g., https://domain.com/users/username)
+     * @throws IllegalArgumentException if handle is invalid or domain is not allowed
+     * @throws IOException if WebFinger request fails
+     */
+    public String discoverActor(String handle) throws IOException {
+        log.debug("Discovering actor for handle: {}", handle);
+
+        // Parse and validate handle
+        ParsedHandle parsed = parseHandle(handle);
+        String username = parsed.username;
+        String domain = parsed.domain;
+
+        // SSRF protection: validate domain
+        validateDomain(domain);
+
+        // Fetch WebFinger resource
+        Map<String, Object> webFingerResponse = fetchWebFingerResource(domain, username);
+
+        // Extract actor URI from links
+        String actorUri = extractActorUri(webFingerResponse);
+        if (actorUri == null) {
+            throw new IOException("No ActivityPub actor link found in WebFinger response");
+        }
+
+        log.info("Discovered actor URI: {} for handle: {}", actorUri, handle);
+        return actorUri;
+    }
+
+    /**
+     * Parses a handle into username and domain components.
+     *
+     * @param handle the handle (e.g., @username@domain or username@domain)
+     * @return parsed handle components
+     * @throws IllegalArgumentException if handle format is invalid
+     */
+    private ParsedHandle parseHandle(String handle) {
+        if (handle == null || handle.isBlank()) {
+            throw new IllegalArgumentException("Handle cannot be null or empty");
+        }
+
+        // Remove leading @ if present
+        String normalized = handle.startsWith("@") ? handle.substring(1) : handle;
+
+        // Split on @
+        String[] parts = normalized.split("@");
+        if (parts.length != 2) {
+            throw new IllegalArgumentException("Invalid handle format. Expected: @username@domain or username@domain");
+        }
+
+        String username = parts[0].trim();
+        String domain = parts[1].trim();
+
+        if (username.isEmpty() || domain.isEmpty()) {
+            throw new IllegalArgumentException("Username and domain cannot be empty");
+        }
+
+        // Validate username format (alphanumeric, underscore, hyphen)
+        if (!username.matches("^[a-zA-Z0-9_-]+$")) {
+            throw new IllegalArgumentException("Invalid username format. Allowed characters: a-z, A-Z, 0-9, _, -");
+        }
+
+        // Validate domain format (basic check - allow domains and IP addresses)
+        // Domain: must have at least one dot and end with 2+ letters
+        // IP: must be 4 numbers separated by dots
+        boolean isValidDomain = domain.matches("^[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$");
+        boolean isValidIP = domain.matches("^\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}$");
+
+        if (!isValidDomain && !isValidIP) {
+            throw new IllegalArgumentException("Invalid domain format");
+        }
+
+        return new ParsedHandle(username, domain);
+    }
+
+    /**
+     * Fetches WebFinger resource from a remote domain.
+     *
+     * @param domain the domain to query
+     * @param username the username to look up
+     * @return WebFinger response as a map
+     * @throws IOException if request fails
+     */
+    private Map<String, Object> fetchWebFingerResource(String domain, String username) throws IOException {
+        // Construct WebFinger URL
+        String resource = "acct:" + username + "@" + domain;
+        String webFingerUrl = "https://" + domain + WEBFINGER_PATH + "?resource=" + resource;
+
+        log.debug("Fetching WebFinger resource: {}", webFingerUrl);
+
+        try {
+            HttpClient client = HttpClient.newBuilder()
+                .connectTimeout(Duration.ofSeconds(TIMEOUT_SECONDS))
+                .followRedirects(HttpClient.Redirect.NORMAL)
+                .build();
+
+            HttpRequest request = HttpRequest.newBuilder()
+                .uri(URI.create(webFingerUrl))
+                .timeout(Duration.ofSeconds(TIMEOUT_SECONDS))
+                .header("Accept", "application/jrd+json, application/json")
+                .GET()
+                .build();
+
+            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
+
+            if (response.statusCode() != 200) {
+                throw new IOException("WebFinger request failed with status: " + response.statusCode());
+            }
+
+            // Parse JSON response
+            @SuppressWarnings("unchecked")
+            Map<String, Object> webFingerData = objectMapper.readValue(response.body(), Map.class);
+
+            return webFingerData;
+
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("WebFinger request interrupted", e);
+        } catch (Exception e) {
+            throw new IOException("Failed to fetch WebFinger resource: " + e.getMessage(), e);
+        }
+    }
+
+    /**
+     * Validates that a domain is not a private or loopback address (SSRF protection).
+     *
+     * @param domain the domain to validate
+     * @throws IllegalArgumentException if domain resolves to a private IP
+     */
+    private void validateDomain(String domain) {
+        // Don't allow requests to local domain (should use local API instead)
+        if (domain.equalsIgnoreCase(localDomain)) {
+            throw new IllegalArgumentException("Cannot discover local users via WebFinger. Use local API instead.");
+        }
+
+        try {
+            InetAddress address = InetAddress.getByName(domain);
+
+            // Block loopback addresses (127.0.0.0/8, ::1)
+            if (address.isLoopbackAddress()) {
+                throw new IllegalArgumentException("Loopback addresses are not allowed: " + domain);
+            }
+
+            // Block site-local addresses (private IPs: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
+            if (address.isSiteLocalAddress()) {
+                throw new IllegalArgumentException("Private IP addresses are not allowed: " + domain);
+            }
+
+            // Block link-local addresses (169.254.0.0/16, fe80::/10)
+            if (address.isLinkLocalAddress()) {
+                throw new IllegalArgumentException("Link-local addresses are not allowed: " + domain);
+            }
+
+            // Block multicast addresses
+            if (address.isMulticastAddress()) {
+                throw new IllegalArgumentException("Multicast addresses are not allowed: " + domain);
+            }
+
+            log.debug("Domain validation passed for: {} (resolved to {})", domain, address.getHostAddress());
+
+        } catch (UnknownHostException e) {
+            throw new IllegalArgumentException("Unable to resolve domain: " + domain, e);
+        }
+    }
+
+    /**
+     * Extracts the ActivityPub actor URI from a WebFinger response.
+     *
+     * @param webFingerResponse the WebFinger response
+     * @return the actor URI, or null if not found
+     */
+    private String extractActorUri(Map<String, Object> webFingerResponse) {
+        Object linksObj = webFingerResponse.get("links");
+        if (!(linksObj instanceof List)) {
+            return null;
+        }
+
+        @SuppressWarnings("unchecked")
+        List<Map<String, Object>> links = (List<Map<String, Object>>) linksObj;
+
+        // Look for link with rel="self" and type="application/activity+json"
+        for (Map<String, Object> link : links) {
+            String rel = (String) link.get("rel");
+            String type = (String) link.get("type");
+            String href = (String) link.get("href");
+
+            if ("self".equals(rel) &&
+                (ACTIVITYPUB_CONTENT_TYPE.equals(type) ||
+                 "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"".equals(type))) {
+                return href;
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Internal class to hold parsed handle components.
+     */
+    private static class ParsedHandle {
+        final String username;
+        final String domain;
+
+        ParsedHandle(String username, String domain) {
+            this.username = username;
+            this.domain = domain;
+        }
+    }
+}
diff --git a/src/main/resources/db/migration/V13__create_remote_activities_table.sql b/src/main/resources/db/migration/V13__create_remote_activities_table.sql
new file mode 100644
index 0000000..b4efe02
--- /dev/null
+++ b/src/main/resources/db/migration/V13__create_remote_activities_table.sql
@@ -0,0 +1,63 @@
+-- Create remote_activities table for storing metadata from federated fitness activities
+-- IMPORTANT: This table stores METADATA ONLY - no full track data
+-- Maps and tracks are referenced via URLs pointing to the origin server
+
+CREATE TABLE IF NOT EXISTS remote_activities (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+
+    -- ActivityPub identifiers
+    activity_uri VARCHAR(512) NOT NULL UNIQUE,
+    remote_actor_uri VARCHAR(512) NOT NULL,
+
+    -- Activity metadata
+    activity_type VARCHAR(50),
+    title VARCHAR(500) NOT NULL,
+    description TEXT,
+    published_at TIMESTAMP NOT NULL,
+
+    -- Fitness metrics
+    total_distance BIGINT,                 -- meters
+    total_duration_seconds BIGINT,         -- seconds
+    elevation_gain INTEGER,                -- meters
+    average_pace_seconds BIGINT,           -- seconds per km
+    average_heart_rate INTEGER,            -- BPM
+    max_speed DOUBLE PRECISION,            -- km/h
+    average_speed DOUBLE PRECISION,        -- km/h
+    calories INTEGER,
+
+    -- Remote URLs (point to origin server)
+    map_image_url VARCHAR(512),            -- URL to static map image
+    track_geojson_url VARCHAR(512),        -- URL to GeoJSON track data (optional)
+
+    -- Visibility
+    visibility VARCHAR(20) NOT NULL,       -- PUBLIC, FOLLOWERS, PRIVATE
+
+    -- Full ActivityPub object as JSONB
+    activitypub_object JSONB,
+
+    -- Timestamps
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    -- Foreign key constraint
+    CONSTRAINT fk_remote_actor FOREIGN KEY (remote_actor_uri)
+        REFERENCES remote_actors(actor_uri) ON DELETE CASCADE
+);
+
+-- Indexes for performance
+CREATE UNIQUE INDEX idx_remote_activity_uri ON remote_activities(activity_uri);
+CREATE INDEX idx_remote_activity_actor ON remote_activities(remote_actor_uri);
+CREATE INDEX idx_remote_activity_published ON remote_activities(published_at DESC);
+CREATE INDEX idx_remote_activity_visibility ON remote_activities(visibility);
+CREATE INDEX idx_remote_activity_type ON remote_activities(activity_type);
+
+-- Index for JSONB queries (if needed in the future)
+CREATE INDEX idx_remote_activity_jsonb ON remote_activities USING gin(activitypub_object);
+
+-- Comment on table
+COMMENT ON TABLE remote_activities IS 'Stores metadata-only for remote fitness activities from federated instances';
+COMMENT ON COLUMN remote_activities.activity_uri IS 'Globally unique ActivityPub activity URI';
+COMMENT ON COLUMN remote_activities.remote_actor_uri IS 'ActivityPub actor URI of the activity creator';
+COMMENT ON COLUMN remote_activities.map_image_url IS 'URL to map image on origin server (no local storage)';
+COMMENT ON COLUMN remote_activities.track_geojson_url IS 'URL to GeoJSON on origin server (optional)';
+COMMENT ON COLUMN remote_activities.activitypub_object IS 'Full ActivityPub object as JSONB for future re-parsing';
diff --git a/src/main/resources/static/js/timeline.js b/src/main/resources/static/js/timeline.js
index 96affb6..08e00b2 100644
--- a/src/main/resources/static/js/timeline.js
+++ b/src/main/resources/static/js/timeline.js
@@ -123,7 +123,7 @@ const FitPubTimeline = {
                                     <a href="/users/${activity.username}" class="text-decoration-none text-muted">
                                         @${this.escapeHtml(activity.username)}
                                     </a>
-                                    ${!activity.isLocal ? ' <i class="bi bi-globe2" title="Federated user"></i>' : ''}
+                                    ${!activity.isLocal ? ' <span class="badge bg-info ms-1" title="Federated Activity"><i class="bi bi-globe2"></i> Remote</span>' : ''}
                                     • ${this.formatTimeAgo(activity.startedAt)}
                                 </div>
                             </div>
@@ -136,9 +136,15 @@ const FitPubTimeline = {
 
                         <!-- Activity Title and Description -->
                         <h5 class="card-title">
-                            <a href="/activities/${activity.id}" class="text-decoration-none text-dark">
-                                ${this.escapeHtml(activity.title || 'Untitled Activity')}
-                            </a>
+                            ${activity.isLocal
+                                ? `<a href="/activities/${activity.id}" class="text-decoration-none text-dark">
+                                    ${this.escapeHtml(activity.title || 'Untitled Activity')}
+                                   </a>`
+                                : `<a href="${activity.activityUri || '#'}" target="_blank" class="text-decoration-none text-dark">
+                                    ${this.escapeHtml(activity.title || 'Untitled Activity')}
+                                    <i class="bi bi-box-arrow-up-right ms-1 small"></i>
+                                   </a>`
+                            }
                         </h5>
 
                         ${activity.description
@@ -171,9 +177,14 @@ const FitPubTimeline = {
                                 <i class="bi bi-heart${activity.likedByCurrentUser ? '-fill' : ''}"></i>
                                 <span class="like-count">${activity.likesCount || 0}</span>
                             </button>
-                            <a href="/activities/${activity.id}" class="btn btn-sm btn-outline-primary">
-                                <i class="bi bi-eye"></i> View Details
-                            </a>
+                            ${activity.isLocal
+                                ? `<a href="/activities/${activity.id}" class="btn btn-sm btn-outline-primary">
+                                    <i class="bi bi-eye"></i> View Details
+                                   </a>`
+                                : `<a href="${activity.activityUri || '#'}" target="_blank" class="btn btn-sm btn-outline-primary">
+                                    <i class="bi bi-box-arrow-up-right"></i> View on Origin Server
+                                   </a>`
+                            }
                             <span class="ms-auto text-muted small d-flex align-items-center gap-2">
                                 ${activity.commentsCount > 0 ? `<span><i class="bi bi-chat-left-text"></i> ${activity.commentsCount}</span>` : ''}
                                 <span>
@@ -284,6 +295,30 @@ const FitPubTimeline = {
             return;
         }
 
+        // Handle remote activities differently - show static map image
+        if (!activity.isLocal) {
+            if (activity.mapImageUrl) {
+                mapElement.innerHTML = `
+                    <div class="position-relative w-100 h-100">
+                        <img src="${this.escapeHtml(activity.mapImageUrl)}"
+                             alt="Activity Map"
+                             class="img-fluid w-100 h-100"
+                             style="object-fit: cover; border-radius: 8px;"
+                             onerror="this.parentElement.innerHTML='<div class=\\'d-flex align-items-center justify-content-center h-100 bg-light\\'><p class=\\'text-muted\\'>Map not available</p></div>'">
+                        <div class="position-absolute top-0 end-0 m-2">
+                            <span class="badge bg-secondary">
+                                <i class="bi bi-globe2"></i> Remote Map
+                            </span>
+                        </div>
+                    </div>
+                `;
+            } else {
+                mapElement.innerHTML = '<div class="d-flex align-items-center justify-content-center h-100 bg-light"><p class="text-muted">No map available for this remote activity</p></div>';
+            }
+            return;
+        }
+
+        // Handle local activities - render interactive Leaflet map
         try {
             // Fetch track data
             const response = await fetch(`/api/activities/${activity.id}/track`);
diff --git a/src/main/resources/templates/users/discover.html b/src/main/resources/templates/users/discover.html
index 25a516c..c79e772 100644
--- a/src/main/resources/templates/users/discover.html
+++ b/src/main/resources/templates/users/discover.html
@@ -17,7 +17,69 @@
                     <h2 class="mb-1">
                         <i class="bi bi-people"></i> Discover Users
                     </h2>
-                    <p class="text-muted">Find and connect with athletes on FitPub</p>
+                    <p class="text-muted">Find and connect with athletes on FitPub and across the Fediverse</p>
+                </div>
+            </div>
+
+            <!-- Remote User Discovery -->
+            <div class="row mb-4">
+                <div class="col-12 col-md-8 col-lg-6">
+                    <div class="card">
+                        <div class="card-body">
+                            <h5 class="card-title mb-3">
+                                <i class="bi bi-globe"></i> Follow Remote Users
+                            </h5>
+                            <p class="text-muted small mb-3">
+                                Connect with users from other FitPub instances or ActivityPub-compatible platforms like Mastodon
+                            </p>
+                            <form id="remoteUserSearchForm">
+                                <div class="input-group">
+                                    <span class="input-group-text">@</span>
+                                    <input type="text"
+                                           class="form-control"
+                                           id="remoteUserHandle"
+                                           placeholder="username@domain.com"
+                                           pattern="[a-zA-Z0-9_]+@[a-zA-Z0-9.-]+"
+                                           autocomplete="off"
+                                           required>
+                                    <button type="submit" class="btn btn-primary">
+                                        <i class="bi bi-search"></i> Search
+                                    </button>
+                                </div>
+                                <div class="form-text">
+                                    Enter a handle like: alice@fitpub.example or bob@mastodon.social
+                                </div>
+                            </form>
+
+                            <!-- Remote User Result -->
+                            <div id="remoteUserResult" class="mt-3 d-none">
+                                <!-- Will be populated by JavaScript -->
+                            </div>
+
+                            <!-- Remote User Error -->
+                            <div id="remoteUserError" class="alert alert-danger mt-3 d-none" role="alert">
+                                <i class="bi bi-exclamation-triangle-fill"></i>
+                                <span id="remoteUserErrorText"></span>
+                            </div>
+
+                            <!-- Remote User Loading -->
+                            <div id="remoteUserLoading" class="text-center mt-3 d-none">
+                                <div class="spinner-border spinner-border-sm text-primary" role="status">
+                                    <span class="visually-hidden">Searching...</span>
+                                </div>
+                                <span class="ms-2 text-muted">Discovering remote user...</span>
+                            </div>
+                        </div>
+                    </div>
+                </div>
+            </div>
+
+            <!-- Local User Search -->
+            <div class="row mb-3">
+                <div class="col-12">
+                    <h5 class="mb-3">
+                        <i class="bi bi-house-door"></i> Local Users
+                    </h5>
                 </div>
             </div>
 
@@ -104,6 +166,13 @@
             const pageSize = 12;
 
             document.addEventListener('DOMContentLoaded', function() {
+                // Remote user search form handler
+                const remoteUserSearchForm = document.getElementById('remoteUserSearchForm');
+                remoteUserSearchForm.addEventListener('submit', async function(e) {
+                    e.preventDefault();
+                    await searchRemoteUser();
+                });
+
                 // Load initial users (browse mode)
                 loadUsers();
 
@@ -158,6 +227,140 @@
                 document.getElementById('searchInfo').classList.add('d-none');
             }
 
+            async function searchRemoteUser() {
+                const handle = document.getElementById('remoteUserHandle').value.trim();
+
+                if (!handle) {
+                    return;
+                }
+
+                // Show loading, hide result and error
+                document.getElementById('remoteUserLoading').classList.remove('d-none');
+                document.getElementById('remoteUserResult').classList.add('d-none');
+                document.getElementById('remoteUserError').classList.add('d-none');
+
+                try {
+                    const response = await FitPubAuth.authenticatedFetch(
+                        `/api/users/discover-remote?handle=${encodeURIComponent(handle)}`
+                    );
+
+                    if (!response.ok) {
+                        if (response.status === 400) {
+                            throw new Error('Invalid handle format. Please use format: username@domain.com');
+                        } else if (response.status === 404) {
+                            throw new Error('User not found. Please check the handle and try again.');
+                        } else {
+                            throw new Error('Failed to discover remote user. Please try again.');
+                        }
+                    }
+
+                    const actor = await response.json();
+
+                    // Hide loading
+                    document.getElementById('remoteUserLoading').classList.add('d-none');
+
+                    // Display remote user
+                    displayRemoteUser(actor);
+
+                } catch (error) {
+                    console.error('Error discovering remote user:', error);
+
+                    // Hide loading
+                    document.getElementById('remoteUserLoading').classList.add('d-none');
+
+                    // Show error
+                    document.getElementById('remoteUserErrorText').textContent = error.message;
+                    document.getElementById('remoteUserError').classList.remove('d-none');
+                }
+            }
+
+            function displayRemoteUser(actor) {
+                const resultDiv = document.getElementById('remoteUserResult');
+
+                const avatarHtml = actor.avatarUrl
+                    ? `<img src="${escapeHtml(actor.avatarUrl)}"
+                            alt="${escapeHtml(actor.username)}"
+                            class="rounded-circle"
+                            width="60"
+                            height="60"
+                            onerror="this.style.display='none'; this.nextElementSibling.style.display='flex';">`
+                    : '';
+
+                const avatarPlaceholder = `
+                    <div class="avatar-placeholder ${actor.avatarUrl ? 'd-none' : ''}"
+                         style="width: 60px; height: 60px;">
+                        <i class="bi bi-person-circle"></i>
+                    </div>
+                `;
+
+                resultDiv.innerHTML = `
+                    <div class="card border-primary">
+                        <div class="card-body">
+                            <div class="d-flex align-items-center mb-3">
+                                <div class="me-3">
+                                    ${avatarHtml}
+                                    ${avatarPlaceholder}
+                                </div>
+                                <div class="flex-grow-1">
+                                    <h6 class="mb-1">${escapeHtml(actor.displayName || actor.username)}</h6>
+                                    <p class="text-muted small mb-0">
+                                        @${escapeHtml(actor.handle)}
+                                        <span class="badge bg-info ms-2">Remote</span>
+                                    </p>
+                                </div>
+                            </div>
+
+                            ${actor.bio
+                                ? `<p class="card-text small mb-3">${escapeHtml(actor.bio)}</p>`
+                                : '<p class="card-text small text-muted mb-3 fst-italic">No bio</p>'
+                            }
+
+                            <div class="d-flex gap-2">
+                                <button class="btn btn-primary" onclick="followRemoteUser('${escapeHtml(actor.handle)}')">
+                                    <i class="bi bi-person-plus"></i> Follow
+                                </button>
+                                ${actor.actorUri
+                                    ? `<a href="${escapeHtml(actor.actorUri)}"
+                                          target="_blank"
+                                          class="btn btn-outline-secondary">
+                                        <i class="bi bi-box-arrow-up-right"></i> View Profile
+                                    </a>`
+                                    : ''
+                                }
+                            </div>
+                        </div>
+                    </div>
+                `;
+
+                resultDiv.classList.remove('d-none');
+            }
+
+            async function followRemoteUser(handle) {
+                try {
+                    const response = await FitPubAuth.authenticatedFetch(
+                        `/api/users/${encodeURIComponent(handle)}/follow`,
+                        { method: 'POST' }
+                    );
+
+                    if (!response.ok) {
+                        throw new Error('Failed to follow user');
+                    }
+
+                    const result = await response.json();
+
+                    // Show success message
+                    FitPub.showAlert('success', result.message || `Follow request sent to ${handle}`);
+
+                    // Clear the search form
+                    document.getElementById('remoteUserHandle').value = '';
+                    document.getElementById('remoteUserResult').classList.add('d-none');
+
+                } catch (error) {
+                    console.error('Error following remote user:', error);
+                    FitPub.showAlert('error', 'Failed to follow user. Please try again.');
+                }
+            }
+
             async function loadUsers() {
                 try {
                     // Show loading
diff --git a/src/test/java/org/operaton/fitpub/integration/FederationFollowFlowIntegrationTest.java b/src/test/java/org/operaton/fitpub/integration/FederationFollowFlowIntegrationTest.java
new file mode 100644
index 0000000..c4bbbb0
--- /dev/null
+++ b/src/test/java/org/operaton/fitpub/integration/FederationFollowFlowIntegrationTest.java
@@ -0,0 +1,418 @@
+package org.operaton.fitpub.integration;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.operaton.fitpub.model.entity.Follow;
+import org.operaton.fitpub.model.entity.RemoteActor;
+import org.operaton.fitpub.model.entity.User;
+import org.operaton.fitpub.repository.FollowRepository;
+import org.operaton.fitpub.repository.RemoteActorRepository;
+import org.operaton.fitpub.repository.UserRepository;
+import org.operaton.fitpub.security.JwtTokenProvider;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.MediaType;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.MvcResult;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.NoSuchAlgorithmException;
+import java.time.Instant;
+import java.util.Base64;
+import java.util.Map;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
+
+/**
+ * Integration tests for the complete federation follow flow.
+ * Tests the entire workflow from following a remote user to receiving accept notifications.
+ */
+@SpringBootTest
+@AutoConfigureMockMvc
+@ActiveProfiles("test")
+@Transactional
+class FederationFollowFlowIntegrationTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Autowired
+    private UserRepository userRepository;
+
+    @Autowired
+    private FollowRepository followRepository;
+
+    @Autowired
+    private RemoteActorRepository remoteActorRepository;
+
+    @Autowired
+    private PasswordEncoder passwordEncoder;
+
+    @Autowired
+    private JwtTokenProvider jwtTokenProvider;
+
+    @Value("${fitpub.base-url}")
+    private String baseUrl;
+
+    private User testUser;
+    private String authToken;
+
+    @BeforeEach
+    void setUp() throws NoSuchAlgorithmException {
+        // Generate RSA key pair for ActivityPub
+        KeyPair keyPair = generateRsaKeyPair();
+        String publicKey = encodePublicKey(keyPair.getPublic().getEncoded());
+        String privateKey = encodePrivateKey(keyPair.getPrivate().getEncoded());
+
+        // Create test user
+        testUser = User.builder()
+            .username("testuser")
+            .email("test@example.com")
+            .passwordHash(passwordEncoder.encode("password123"))
+            .displayName("Test User")
+            .publicKey(publicKey)
+            .privateKey(privateKey)
+            .enabled(true)
+            .build();
+        testUser = userRepository.save(testUser);
+
+        // Generate JWT token
+        authToken = jwtTokenProvider.createToken(testUser.getUsername());
+    }
+
+    private KeyPair generateRsaKeyPair() throws NoSuchAlgorithmException {
+        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
+        keyGen.initialize(2048);
+        return keyGen.generateKeyPair();
+    }
+
+    private String encodePublicKey(byte[] keyBytes) {
+        String base64 = Base64.getEncoder().encodeToString(keyBytes);
+        return "-----BEGIN PUBLIC KEY-----\n" + base64 + "\n-----END PUBLIC KEY-----";
+    }
+
+    private String encodePrivateKey(byte[] keyBytes) {
+        String base64 = Base64.getEncoder().encodeToString(keyBytes);
+        return "-----BEGIN PRIVATE KEY-----\n" + base64 + "\n-----END PRIVATE KEY-----";
+    }
+
+    @Test
+    @Disabled("Requires mocking external HTTP calls to WebFinger and remote ActivityPub servers")
+    @DisplayName("Should follow a remote user via handle format @username@domain")
+    void testFollowRemoteUserWithHandle() throws Exception {
+        String remoteHandle = "@alice@fitpub.example";
+
+        // Perform follow request
+        MvcResult result = mockMvc.perform(post("/api/users/" + remoteHandle + "/follow")
+                .header("Authorization", "Bearer " + authToken)
+                .contentType(MediaType.APPLICATION_JSON))
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("$.status").value("PENDING"))
+            .andReturn();
+
+        // Verify follow record was created with PENDING status
+        String actorUri = baseUrl + "/users/alice"; // Would be resolved via WebFinger in real scenario
+        Follow follow = followRepository.findByFollowerIdAndFollowingActorUri(testUser.getId(), actorUri)
+            .orElse(null);
+
+        // Note: In a real scenario, this would require mocking WebFinger discovery
+        // For now, we verify the endpoint accepts the format
+        assertThat(result.getResponse().getContentAsString()).contains("PENDING");
+    }
+
+    @Test
+    @DisplayName("Should process incoming Follow activity and create follow relationship")
+    void testProcessIncomingFollowActivity() throws Exception {
+        // Create a remote actor
+        RemoteActor remoteActor = RemoteActor.builder()
+            .actorUri("https://remote.example/users/bob")
+            .username("bob")
+            .domain("remote.example")
+            .displayName("Bob Remote")
+            .inboxUrl("https://remote.example/users/bob/inbox")
+            .outboxUrl("https://remote.example/users/bob/outbox")
+            .publicKey("-----BEGIN PUBLIC KEY-----\ntest\n-----END PUBLIC KEY-----")
+            .lastFetchedAt(Instant.now())
+            .build();
+        remoteActor = remoteActorRepository.save(remoteActor);
+
+        // Create Follow activity
+        String followId = "https://remote.example/activities/follow/" + UUID.randomUUID();
+        Map<String, Object> followActivity = Map.of(
+            "@context", "https://www.w3.org/ns/activitystreams",
+            "type", "Follow",
+            "id", followId,
+            "actor", remoteActor.getActorUri(),
+            "object", baseUrl + "/users/" + testUser.getUsername(),
+            "published", Instant.now().toString()
+        );
+
+        // Post to inbox (without signature validation for test)
+        mockMvc.perform(post("/users/" + testUser.getUsername() + "/inbox")
+                .contentType("application/activity+json")
+                .content(objectMapper.writeValueAsString(followActivity)))
+            .andExpect(status().isAccepted());
+
+        // Verify follow relationship was created
+        Follow follow = followRepository.findByRemoteActorUriAndFollowingActorUri(
+            remoteActor.getActorUri(),
+            baseUrl + "/users/" + testUser.getUsername()
+        ).orElse(null);
+
+        assertThat(follow).isNotNull();
+        assertThat(follow.getStatus()).isEqualTo(Follow.FollowStatus.ACCEPTED);
+    }
+
+    @Test
+    @DisplayName("Should process Accept activity and update follow status to ACCEPTED")
+    void testProcessAcceptActivity() throws Exception {
+        // Create a remote actor
+        RemoteActor remoteActor = RemoteActor.builder()
+            .actorUri("https://remote.example/users/carol")
+            .username("carol")
+            .domain("remote.example")
+            .displayName("Carol Remote")
+            .inboxUrl("https://remote.example/users/carol/inbox")
+            .outboxUrl("https://remote.example/users/carol/outbox")
+            .publicKey("-----BEGIN PUBLIC KEY-----\ntest\n-----END PUBLIC KEY-----")
+            .lastFetchedAt(Instant.now())
+            .build();
+        remoteActor = remoteActorRepository.save(remoteActor);
+
+        // Create pending follow
+        String followActivityId = baseUrl + "/activities/follow/" + UUID.randomUUID();
+        Follow pendingFollow = Follow.builder()
+            .followerId(testUser.getId())
+            .followingActorUri(remoteActor.getActorUri())
+            .status(Follow.FollowStatus.PENDING)
+            .activityId(followActivityId)
+            .build();
+        pendingFollow = followRepository.save(pendingFollow);
+
+        // Create Accept activity
+        Map<String, Object> acceptActivity = Map.of(
+            "@context", "https://www.w3.org/ns/activitystreams",
+            "type", "Accept",
+            "id", "https://remote.example/activities/accept/" + UUID.randomUUID(),
+            "actor", remoteActor.getActorUri(),
+            "object", followActivityId
+        );
+
+        // Post Accept to inbox
+        mockMvc.perform(post("/users/" + testUser.getUsername() + "/inbox")
+                .contentType("application/activity+json")
+                .content(objectMapper.writeValueAsString(acceptActivity)))
+            .andExpect(status().isAccepted());
+
+        // Verify follow status was updated to ACCEPTED
+        Follow updatedFollow = followRepository.findById(pendingFollow.getId()).orElseThrow();
+        assertThat(updatedFollow.getStatus()).isEqualTo(Follow.FollowStatus.ACCEPTED);
+    }
+
+    @Test
+    @DisplayName("Should process Undo Follow activity and remove follow relationship")
+    void testProcessUndoFollowActivity() throws Exception {
+        // Create a remote actor
+        RemoteActor remoteActor = RemoteActor.builder()
+            .actorUri("https://remote.example/users/dave")
+            .username("dave")
+            .domain("remote.example")
+            .displayName("Dave Remote")
+            .inboxUrl("https://remote.example/users/dave/inbox")
+            .outboxUrl("https://remote.example/users/dave/outbox")
+            .publicKey("-----BEGIN PUBLIC KEY-----\ntest\n-----END PUBLIC KEY-----")
+            .lastFetchedAt(Instant.now())
+            .build();
+        remoteActor = remoteActorRepository.save(remoteActor);
+
+        // Create accepted follow
+        Follow acceptedFollow = Follow.builder()
+            .remoteActorUri(remoteActor.getActorUri())
+            .followingActorUri(baseUrl + "/users/" + testUser.getUsername())
+            .status(Follow.FollowStatus.ACCEPTED)
+            .build();
+        acceptedFollow = followRepository.save(acceptedFollow);
+
+        // Create Undo Follow activity
+        Map<String, Object> undoActivity = Map.of(
+            "@context", "https://www.w3.org/ns/activitystreams",
+            "type", "Undo",
+            "id", "https://remote.example/activities/undo/" + UUID.randomUUID(),
+            "actor", remoteActor.getActorUri(),
+            "object", Map.of(
+                "type", "Follow",
+                "actor", remoteActor.getActorUri(),
+                "object", baseUrl + "/users/" + testUser.getUsername()
+            )
+        );
+
+        // Post Undo to inbox
+        mockMvc.perform(post("/users/" + testUser.getUsername() + "/inbox")
+                .contentType("application/activity+json")
+                .content(objectMapper.writeValueAsString(undoActivity)))
+            .andExpect(status().isAccepted());
+
+        // Verify follow was deleted
+        boolean followExists = followRepository.existsById(acceptedFollow.getId());
+        assertThat(followExists).isFalse();
+    }
+
+    @Test
+    @DisplayName("Should return followers list including both local and remote followers")
+    void testGetFollowersList() throws Exception {
+        // Generate keypair for local follower
+        KeyPair keyPair = generateRsaKeyPair();
+
+        // Create a local follower
+        User localFollower = User.builder()
+            .username("localfollower")
+            .email("local@example.com")
+            .passwordHash(passwordEncoder.encode("password"))
+            .displayName("Local Follower")
+            .publicKey(encodePublicKey(keyPair.getPublic().getEncoded()))
+            .privateKey(encodePrivateKey(keyPair.getPrivate().getEncoded()))
+            .enabled(true)
+            .build();
+        localFollower = userRepository.save(localFollower);
+
+        Follow localFollow = Follow.builder()
+            .followerId(localFollower.getId())
+            .followingActorUri(baseUrl + "/users/" + testUser.getUsername())
+            .status(Follow.FollowStatus.ACCEPTED)
+            .build();
+        followRepository.save(localFollow);
+
+        // Create a remote follower
+        RemoteActor remoteFollower = RemoteActor.builder()
+            .actorUri("https://remote.example/users/eve")
+            .username("eve")
+            .domain("remote.example")
+            .displayName("Eve Remote")
+            .inboxUrl("https://remote.example/users/eve/inbox")
+            .outboxUrl("https://remote.example/users/eve/outbox")
+            .publicKey("-----BEGIN PUBLIC KEY-----\ntest\n-----END PUBLIC KEY-----")
+            .lastFetchedAt(Instant.now())
+            .build();
+        remoteFollower = remoteActorRepository.save(remoteFollower);
+
+        Follow remoteFollow = Follow.builder()
+            .remoteActorUri(remoteFollower.getActorUri())
+            .followingActorUri(baseUrl + "/users/" + testUser.getUsername())
+            .status(Follow.FollowStatus.ACCEPTED)
+            .build();
+        followRepository.save(remoteFollow);
+
+        // Get followers list
+        mockMvc.perform(get("/api/users/" + testUser.getUsername() + "/followers"))
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("$.length()").value(2))
+            .andExpect(jsonPath("$[?(@.username == 'localfollower')]").exists())
+            .andExpect(jsonPath("$[?(@.username == 'eve')]").exists())
+            .andExpect(jsonPath("$[?(@.local == true)]").exists())
+            .andExpect(jsonPath("$[?(@.local == false)]").exists());
+    }
+
+    @Test
+    @DisplayName("Should return following list including both local and remote users")
+    void testGetFollowingList() throws Exception {
+        // Generate keypair for local followed user
+        KeyPair keyPair = generateRsaKeyPair();
+
+        // Create a local user being followed
+        User localFollowed = User.builder()
+            .username("localfollowed")
+            .email("followed@example.com")
+            .passwordHash(passwordEncoder.encode("password"))
+            .displayName("Local Followed")
+            .publicKey(encodePublicKey(keyPair.getPublic().getEncoded()))
+            .privateKey(encodePrivateKey(keyPair.getPrivate().getEncoded()))
+            .enabled(true)
+            .build();
+        localFollowed = userRepository.save(localFollowed);
+
+        Follow localFollow = Follow.builder()
+            .followerId(testUser.getId())
+            .followingActorUri(baseUrl + "/users/" + localFollowed.getUsername())
+            .status(Follow.FollowStatus.ACCEPTED)
+            .build();
+        followRepository.save(localFollow);
+
+        // Create a remote user being followed
+        RemoteActor remoteFollowed = RemoteActor.builder()
+            .actorUri("https://remote.example/users/frank")
+            .username("frank")
+            .domain("remote.example")
+            .displayName("Frank Remote")
+            .inboxUrl("https://remote.example/users/frank/inbox")
+            .outboxUrl("https://remote.example/users/frank/outbox")
+            .publicKey("-----BEGIN PUBLIC KEY-----\ntest\n-----END PUBLIC KEY-----")
+            .lastFetchedAt(Instant.now())
+            .build();
+        remoteFollowed = remoteActorRepository.save(remoteFollowed);
+
+        Follow remoteFollow = Follow.builder()
+            .followerId(testUser.getId())
+            .followingActorUri(remoteFollowed.getActorUri())
+            .status(Follow.FollowStatus.ACCEPTED)
+            .build();
+        followRepository.save(remoteFollow);
+
+        // Get following list
+        mockMvc.perform(get("/api/users/" + testUser.getUsername() + "/following"))
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("$.length()").value(2))
+            .andExpect(jsonPath("$[?(@.username == 'localfollowed')]").exists())
+            .andExpect(jsonPath("$[?(@.username == 'frank')]").exists())
+            .andExpect(jsonPath("$[?(@.local == true)]").exists())
+            .andExpect(jsonPath("$[?(@.local == false)]").exists());
+    }
+
+    @Test
+    @Disabled("Requires mocking external HTTP calls to WebFinger and remote ActivityPub servers")
+    @DisplayName("Should prevent duplicate follow relationships")
+    void testPreventDuplicateFollows() throws Exception {
+        // Create a remote actor
+        RemoteActor remoteActor = RemoteActor.builder()
+            .actorUri("https://remote.example/users/grace")
+            .username("grace")
+            .domain("remote.example")
+            .displayName("Grace Remote")
+            .inboxUrl("https://remote.example/users/grace/inbox")
+            .outboxUrl("https://remote.example/users/grace/outbox")
+            .publicKey("-----BEGIN PUBLIC KEY-----\ntest\n-----END PUBLIC KEY-----")
+            .lastFetchedAt(Instant.now())
+            .build();
+        remoteActor = remoteActorRepository.save(remoteActor);
+
+        // Create existing follow
+        Follow existingFollow = Follow.builder()
+            .followerId(testUser.getId())
+            .followingActorUri(remoteActor.getActorUri())
+            .status(Follow.FollowStatus.ACCEPTED)
+            .build();
+        followRepository.save(existingFollow);
+
+        // Try to follow again - should get appropriate response
+        String remoteHandle = "@grace@remote.example";
+
+        mockMvc.perform(post("/api/users/" + remoteHandle + "/follow")
+                .header("Authorization", "Bearer " + authToken)
+                .contentType(MediaType.APPLICATION_JSON))
+            .andExpect(status().is4xxClientError()); // Should return error for duplicate follow
+    }
+}
diff --git a/src/test/java/org/operaton/fitpub/service/TrainingLoadServiceTest.java b/src/test/java/org/operaton/fitpub/service/TrainingLoadServiceTest.java
index a8369c0..8add6da 100644
--- a/src/test/java/org/operaton/fitpub/service/TrainingLoadServiceTest.java
+++ b/src/test/java/org/operaton/fitpub/service/TrainingLoadServiceTest.java
@@ -280,19 +280,27 @@ class TrainingLoadServiceTest {
         // Given
         int days = 30;
         LocalDate startDate = LocalDate.now().minusDays(days - 1);
-        List<TrainingLoad> expectedLoad = List.of(
+        List<TrainingLoad> existingLoad = List.of(
                 createTrainingLoad(userId, testDate, BigDecimal.valueOf(100.0))
         );
 
         when(trainingLoadRepository.findByUserIdSinceDate(userId, startDate))
-                .thenReturn(expectedLoad);
+                .thenReturn(existingLoad);
 
         // When
         List<TrainingLoad> result = trainingLoadService.getRecentTrainingLoad(userId, days);
 
         // Then
-        assertEquals(expectedLoad, result);
+        // Should return 30 days of data (fills in missing days with rest day entries)
+        assertEquals(30, result.size());
         verify(trainingLoadRepository).findByUserIdSinceDate(userId, startDate);
+
+        // Verify that the existing load is included
+        assertTrue(result.stream().anyMatch(tl ->
+            tl.getDate().equals(testDate) &&
+            tl.getTrainingStressScore() != null &&
+            tl.getTrainingStressScore().compareTo(BigDecimal.valueOf(100.0)) == 0
+        ));
     }
 
     @Test
diff --git a/src/test/java/org/operaton/fitpub/service/WebFingerClientTest.java b/src/test/java/org/operaton/fitpub/service/WebFingerClientTest.java
new file mode 100644
index 0000000..8e1d8b6
--- /dev/null
+++ b/src/test/java/org/operaton/fitpub/service/WebFingerClientTest.java
@@ -0,0 +1,217 @@
+package org.operaton.fitpub.service;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.test.util.ReflectionTestUtils;
+
+import java.io.IOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/**
+ * Unit tests for WebFingerClient.
+ */
+@ExtendWith(MockitoExtension.class)
+class WebFingerClientTest {
+
+    private WebFingerClient webFingerClient;
+    private ObjectMapper objectMapper;
+
+    @BeforeEach
+    void setUp() {
+        objectMapper = new ObjectMapper();
+        webFingerClient = new WebFingerClient(objectMapper);
+        ReflectionTestUtils.setField(webFingerClient, "localDomain", "fitpub.test");
+    }
+
+    // ==================== Handle Parsing Tests ====================
+
+    @Test
+    void parseHandle_withAtPrefix_shouldParseCorrectly() throws Exception {
+        // This test uses reflection to access the private parseHandle method
+        String handle = "@alice@example.com";
+
+        // We can't directly test private methods, but we can test through discoverActor
+        // which will validate the handle parsing logic
+        // For now, we'll test the validation through discoverActor's exceptions
+
+        // Testing valid format doesn't throw during parsing phase
+        assertThatThrownBy(() -> webFingerClient.discoverActor(handle))
+            .isInstanceOf(IOException.class) // Will fail at network call, but parsing succeeded
+            .hasMessageContaining("Failed to fetch WebFinger resource");
+    }
+
+    @Test
+    void parseHandle_withoutAtPrefix_shouldParseCorrectly() throws Exception {
+        String handle = "alice@example.com";
+
+        assertThatThrownBy(() -> webFingerClient.discoverActor(handle))
+            .isInstanceOf(IOException.class) // Will fail at network call, but parsing succeeded
+            .hasMessageContaining("Failed to fetch WebFinger resource");
+    }
+
+    @Test
+    void parseHandle_withNullHandle_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor(null))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Handle cannot be null or empty");
+    }
+
+    @Test
+    void parseHandle_withEmptyHandle_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor(""))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Handle cannot be null or empty");
+    }
+
+    @Test
+    void parseHandle_withBlankHandle_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("   "))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Handle cannot be null or empty");
+    }
+
+    @Test
+    void parseHandle_withoutAtSymbol_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("aliceexample.com"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid handle format");
+    }
+
+    @Test
+    void parseHandle_withMultipleAtSymbols_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("@alice@example@com"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid handle format");
+    }
+
+    @Test
+    void parseHandle_withEmptyUsername_shouldThrowException() {
+        // "@example.com" becomes "example.com" after removing @, then split gives only 1 part
+        assertThatThrownBy(() -> webFingerClient.discoverActor("@example.com"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid handle format");
+    }
+
+    @Test
+    void parseHandle_withEmptyDomain_shouldThrowException() {
+        // "alice@" splits into ["alice"] (trailing empty string is discarded)
+        // So this fails the parts.length != 2 check
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid handle format");
+    }
+
+    @Test
+    void parseHandle_withInvalidUsernameCharacters_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice!@example.com"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid username format");
+    }
+
+    @Test
+    void parseHandle_withInvalidDomainFormat_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@invalid"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid domain format");
+    }
+
+    @Test
+    void parseHandle_withValidUsernameCharacters_shouldNotThrowParsingException() {
+        // Valid characters: a-z, A-Z, 0-9, _, -
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice_bob-123@example.com"))
+            .isInstanceOf(IOException.class) // Fails at network, not parsing
+            .hasMessageContaining("Failed to fetch WebFinger resource");
+    }
+
+    // ==================== SSRF Protection Tests ====================
+
+    @Test
+    void validateDomain_withLoopbackAddress_shouldThrowException() {
+        // "localhost" doesn't have a dot, so it fails domain format validation
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@localhost"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Invalid domain format");
+    }
+
+    @Test
+    void validateDomain_with127_0_0_1_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@127.0.0.1"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Loopback addresses are not allowed");
+    }
+
+    @Test
+    void validateDomain_withPrivateIP_10_0_0_1_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@10.0.0.1"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Private IP addresses are not allowed");
+    }
+
+    @Test
+    void validateDomain_withPrivateIP_192_168_1_1_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@192.168.1.1"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Private IP addresses are not allowed");
+    }
+
+    @Test
+    void validateDomain_withPrivateIP_172_16_0_1_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@172.16.0.1"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Private IP addresses are not allowed");
+    }
+
+    @Test
+    void validateDomain_withLinkLocalAddress_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@169.254.0.1"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Link-local addresses are not allowed");
+    }
+
+    @Test
+    void validateDomain_withLocalDomain_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@fitpub.test"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Cannot discover local users via WebFinger");
+    }
+
+    @Test
+    void validateDomain_withLocalDomainCaseInsensitive_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@FITPUB.TEST"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Cannot discover local users via WebFinger");
+    }
+
+    @Test
+    void validateDomain_withNonexistentDomain_shouldThrowException() {
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@this-domain-does-not-exist-12345.invalid"))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("Unable to resolve domain");
+    }
+
+    // ==================== Integration-like Tests ====================
+    // Note: These tests will attempt real network calls and will fail with IOException
+    // In a real scenario, we'd use WireMock or similar to mock HTTP responses
+
+    @Test
+    void discoverActor_withValidHandle_butNoNetwork_shouldThrowIOException() {
+        // This test validates that valid handles pass validation
+        // Use a domain that definitely won't have WebFinger endpoint
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@example.com"))
+            .isInstanceOf(IOException.class)
+            .hasMessageContaining("Failed to fetch WebFinger resource");
+    }
+
+    @Test
+    void discoverActor_withPublicIP_shouldPassSSRFValidation() {
+        // Public IP (Google DNS) should pass SSRF validation but fail at WebFinger layer
+        assertThatThrownBy(() -> webFingerClient.discoverActor("alice@8.8.8.8"))
+            .isInstanceOf(IOException.class)
+            .hasMessageContaining("Failed to fetch WebFinger resource");
+    }
+}
diff --git a/src/test/resources/application-test.yml b/src/test/resources/application-test.yml
new file mode 100644
index 0000000..8df8581
--- /dev/null
+++ b/src/test/resources/application-test.yml
@@ -0,0 +1,52 @@
+spring:
+  application:
+    name: fitpub-test
+
+  # Testcontainers will automatically configure the datasource
+  datasource:
+    driver-class-name: org.testcontainers.jdbc.ContainerDatabaseDriver
+    url: jdbc:tc:postgis:13-3.1:///testdb?TC_INITSCRIPT=file:src/test/resources/init-test-db.sql
+
+  jpa:
+    hibernate:
+      ddl-auto: validate
+    properties:
+      hibernate:
+        dialect: org.hibernate.spatial.dialect.postgis.PostgisPG10Dialect
+        format_sql: true
+    show-sql: false
+
+  flyway:
+    enabled: true
+    baseline-on-migrate: true
+    locations: classpath:db/migration
+
+  servlet:
+    multipart:
+      max-file-size: 50MB
+      max-request-size: 50MB
+
+fitpub:
+  domain: localhost:8080
+  base-url: http://localhost:8080
+  activitypub:
+    enabled: true
+    max-federation-retries: 3
+  security:
+    jwt:
+      secret: test-secret-key-for-jwt-token-generation-in-tests-must-be-long-enough
+      expiration: 86400000 # 24 hours
+  storage:
+    fit-files:
+      path: ${java.io.tmpdir}/fitpub-test/fit-files
+      retention-days: 365
+  weather:
+    enabled: false
+    api-key: test-api-key
+
+logging:
+  level:
+    org.operaton.fitpub: DEBUG
+    org.springframework: WARN
+    org.hibernate: WARN
+    org.testcontainers: INFO
diff --git a/src/test/resources/init-test-db.sql b/src/test/resources/init-test-db.sql
new file mode 100644
index 0000000..0a2dc09
--- /dev/null
+++ b/src/test/resources/init-test-db.sql
@@ -0,0 +1,2 @@
+-- Initialize PostGIS extension for test database
+CREATE EXTENSION IF NOT EXISTS postgis;