docs: provide complete TaskAuthorizationProvider example (#1146)

* docs: make authorization example complete
* docs: share ownership checks in authorization examples

This fixes #1143

Author: hutiefang76

docs/content/dev/authorization.md

@@ -13,17 +13,34 @@ layout: page
 Implement `TaskAuthorizationProvider` to control per-user access:
 
 ```java
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import jakarta.enterprise.context.ApplicationScoped;
+
+import org.a2aproject.sdk.server.ServerCallContext;
+import org.a2aproject.sdk.server.auth.TaskAuthorizationProvider;
+import org.a2aproject.sdk.server.auth.TaskOperation;
+
 @ApplicationScoped
 public class MyTaskAuthorizationProvider implements TaskAuthorizationProvider {
+    private final ConcurrentMap<String, String> ownershipStore = new ConcurrentHashMap<>();
 
     @Override
     public boolean checkRead(ServerCallContext context, String taskId, TaskOperation op) {
-        return isOwner(context.getUser(), taskId);
+        return isOwner(context, taskId);
+    }
+
+    private boolean isOwner(ServerCallContext context, String taskId) {
+        String owner = ownershipStore.get(taskId);
+        return owner != null
+                && context.getUser() != null
+                && owner.equals(context.getUser().getUsername());
     }
 
     @Override
     public boolean checkWrite(ServerCallContext context, String taskId, TaskOperation op) {
-        return isOwner(context.getUser(), taskId);
+        return isOwner(context, taskId);
     }
 
     @Override
@@ -39,7 +56,7 @@ public class MyTaskAuthorizationProvider implements TaskAuthorizationProvider {
     @Override
     public void recordOwnership(ServerCallContext context, String taskId, TaskOperation op) {
         if (context.getUser() != null) {
-            ownershipStore.put(taskId, context.getUser().getUsername());
+            ownershipStore.putIfAbsent(taskId, context.getUser().getUsername());
         }
     }
 }

server-common/src/main/java/org/a2aproject/sdk/server/auth/TaskAuthorizationProvider.java

@@ -21,34 +21,51 @@
  * configuration is required.
  *
  * <pre>{@code
+ * import java.util.concurrent.ConcurrentHashMap;
+ * import java.util.concurrent.ConcurrentMap;
+ *
+ * import jakarta.enterprise.context.ApplicationScoped;
+ *
+ * import org.a2aproject.sdk.server.ServerCallContext;
+ * import org.a2aproject.sdk.server.auth.TaskAuthorizationProvider;
+ * import org.a2aproject.sdk.server.auth.TaskOperation;
+ *
  * @ApplicationScoped
  * public class MyTaskAuthorizationProvider implements TaskAuthorizationProvider {
+ *     private final ConcurrentMap<String, String> ownershipStore = new ConcurrentHashMap<>();
  *
  *     @Override
  *     public boolean checkRead(ServerCallContext context, String taskId, TaskOperation op) {
- *         User user = context.getUser();
- *         // look up ownership in your backing store
- *         return isOwner(user, taskId);
+ *         return isOwner(context, taskId);
+ *     }
+ *
+ *     private boolean isOwner(ServerCallContext context, String taskId) {
+ *         String owner = ownershipStore.get(taskId);
+ *         return owner != null
+ *                 && context.getUser() != null
+ *                 && owner.equals(context.getUser().getUsername());
  *     }
  *
  *     @Override
  *     public boolean checkWrite(ServerCallContext context, String taskId, TaskOperation op) {
- *         return checkRead(context, taskId, op); // same rule
+ *         return isOwner(context, taskId);
  *     }
  *
  *     @Override
  *     public boolean checkCreate(ServerCallContext context, TaskOperation op) {
- *         return context.getUser().isAuthenticated();
+ *         return context.getUser() != null && context.getUser().isAuthenticated();
  *     }
  *
  *     @Override
  *     public boolean isTaskRecorded(String taskId) {
- *         return ownershipStore.contains(taskId);
+ *         return ownershipStore.containsKey(taskId);
  *     }
  *
  *     @Override
  *     public void recordOwnership(ServerCallContext context, String taskId, TaskOperation op) {
- *         ownershipStore.put(taskId, context.getUser().getUsername());
+ *         if (context.getUser() != null) {
+ *             ownershipStore.putIfAbsent(taskId, context.getUser().getUsername());
+ *         }
  *     }
  * }
  * }</pre>