Add AuthSettings.validate_token_resource to check a bearer token's resource (#3447)

examples/servers/simple-auth/mcp_simple_auth/server.py

@@ -71,6 +71,7 @@ def create_resource_server(settings: ResourceServerSettings) -> MCPServer:
             issuer_url=settings.auth_server_url,
             required_scopes=[settings.mcp_scope],
             resource_server_url=settings.server_url,
+            validate_token_resource=True,  # tokens must be reported as issued for server_url
         ),
     )
     # Store settings for later use in run()

examples/servers/simple-auth/mcp_simple_auth/token_verifier.py

@@ -69,12 +69,19 @@ class IntrospectionTokenVerifier(TokenVerifier):
                     logger.warning(f"Token resource validation failed. Expected: {self.resource_url}")
                     return None
 
+                # `aud` may be a string or a list; report the entry naming this server when there is
+                # one, otherwise what the token was issued for, so the server can compare it.
+                aud: str | list[str] | None = data.get("aud")
+                audiences = aud if isinstance(aud, list) else [aud] if aud else []
+                own = self.resource_url.rstrip("/")
+                resource = next((a for a in audiences if a.rstrip("/") == own), audiences[0] if audiences else None)
+
                 return AccessToken(
                     token=token,
                     client_id=data.get("client_id", "unknown"),
                     scopes=data.get("scope", "").split() if data.get("scope") else [],
                     expires_at=data.get("exp"),
-                    resource=data.get("aud"),  # Include resource in token
+                    resource=resource,
                     subject=data.get("sub"),  # RFC 7662 subject (resource owner)
                     claims=data,
                 )

examples/snippets/servers/oauth_server.py

@@ -24,8 +24,9 @@ mcp = MCPServer(
     # Auth settings for RFC 9728 Protected Resource Metadata
     auth=AuthSettings(
         issuer_url=AnyHttpUrl("https://auth.example.com"),  # Authorization Server URL
-        resource_server_url=AnyHttpUrl("http://localhost:3001"),  # This server's URL
+        resource_server_url=AnyHttpUrl("http://127.0.0.1:8000/mcp"),  # This server's URL (mcp.run() default)
         required_scopes=["user"],
+        validate_token_resource=True,
     ),
 )
 

examples/stories/_shared/auth.py

@@ -169,4 +169,5 @@ def auth_settings(
         required_scopes=scopes,
         client_registration_options=ClientRegistrationOptions(enabled=True, valid_scopes=scopes, default_scopes=scopes),
         identity_assertion_enabled=identity_assertion_enabled,
+        validate_token_resource=True,
     )

examples/stories/bearer_auth/server.py

@@ -28,6 +28,7 @@ class StaticTokenVerifier(TokenVerifier):
             client_id="demo-client",
             scopes=[REQUIRED_SCOPE],
             expires_at=int(time.time()) + 3600,
+            resource=RESOURCE_URL,
             subject="demo-user",
         )
 
@@ -40,6 +41,7 @@ def build_app() -> Starlette:
             issuer_url=AnyHttpUrl(ISSUER),
             resource_server_url=AnyHttpUrl(RESOURCE_URL),
             required_scopes=[REQUIRED_SCOPE],
+            validate_token_resource=True,
         ),
     )
 

examples/stories/bearer_auth/server_lowlevel.py

@@ -46,6 +46,7 @@ def build_app() -> Starlette:
             issuer_url=AnyHttpUrl(ISSUER),
             resource_server_url=AnyHttpUrl(RESOURCE_URL),
             required_scopes=[REQUIRED_SCOPE],
+            validate_token_resource=True,
         ),
         token_verifier=StaticTokenVerifier(),
         transport_security=NO_DNS_REBIND,

examples/stories/oauth_client_credentials/server.py

@@ -66,7 +66,14 @@ def build_app() -> Starlette:
         if creds != f"{DEMO_CLIENT_ID}:{DEMO_CLIENT_SECRET}":
             return JSONResponse({"error": "invalid_client"}, status_code=401)
         access = f"access_{secrets.token_hex(16)}"
-        issued[access] = AccessToken(token=access, client_id=DEMO_CLIENT_ID, scopes=[DEMO_SCOPE], expires_at=None)
+        resource = form.get("resource")  # RFC 8707: bind the token to the resource the client asked for
+        issued[access] = AccessToken(
+            token=access,
+            client_id=DEMO_CLIENT_ID,
+            scopes=[DEMO_SCOPE],
+            expires_at=None,
+            resource=resource if isinstance(resource, str) else None,
+        )
         body = OAuthToken(access_token=access, token_type="Bearer", expires_in=3600, scope=DEMO_SCOPE)
         return JSONResponse(body.model_dump(exclude_none=True), headers={"cache-control": "no-store"})
 

examples/stories/oauth_client_credentials/server_lowlevel.py

@@ -63,7 +63,14 @@ def build_app() -> Starlette:
         if creds != f"{DEMO_CLIENT_ID}:{DEMO_CLIENT_SECRET}":
             return JSONResponse({"error": "invalid_client"}, status_code=401)
         access = f"access_{secrets.token_hex(16)}"
-        issued[access] = AccessToken(token=access, client_id=DEMO_CLIENT_ID, scopes=[DEMO_SCOPE], expires_at=None)
+        resource = form.get("resource")  # RFC 8707: bind the token to the resource the client asked for
+        issued[access] = AccessToken(
+            token=access,
+            client_id=DEMO_CLIENT_ID,
+            scopes=[DEMO_SCOPE],
+            expires_at=None,
+            resource=resource if isinstance(resource, str) else None,
+        )
         body = OAuthToken(access_token=access, token_type="Bearer", expires_in=3600, scope=DEMO_SCOPE)
         return JSONResponse(body.model_dump(exclude_none=True), headers={"cache-control": "no-store"})