Expose the middleware chain on MCPServer and stop sending unrequested change notifications (#3201)

docs_src/subscriptions/tutorial006.py

@@ -0,0 +1,38 @@
+from mcp_types import INVALID_REQUEST, SubscriptionsListenRequestParams
+
+from mcp.server.auth.middleware.auth_context import get_access_token
+from mcp.server.context import CallNext, HandlerResult, ServerRequestContext
+from mcp.server.mcpserver import MCPServer
+from mcp.shared.exceptions import MCPError
+
+# Who may see each file. Replace this table with a database or your RBAC system.
+ACCESS = {
+    "files://report.pdf": {"alice", "bob"},
+    "files://payroll.csv": {"carol"},
+}
+
+
+def can_access(user: str | None, uri: str) -> bool:
+    return user is not None and user in ACCESS.get(uri, set())
+
+
+async def gate_subscriptions(ctx: ServerRequestContext, call_next: CallNext) -> HandlerResult:
+    if ctx.method == "subscriptions/listen":
+        params = SubscriptionsListenRequestParams.model_validate(ctx.params or {}, by_name=False)
+        token = get_access_token()
+        user = token.subject if token else None
+        if not all(can_access(user, uri) for uri in params.notifications.resource_subscriptions or ()):
+            raise MCPError(INVALID_REQUEST, "not permitted to watch the requested resources")
+    return await call_next(ctx)
+
+
+mcp = MCPServer("Reports", middleware=[gate_subscriptions])
+
+
+@mcp.resource("files://{name}")
+def file(name: str) -> str:
+    uri = f"files://{name}"
+    token = get_access_token()
+    if not can_access(token.subject if token else None, uri):
+        raise MCPError(INVALID_REQUEST, f"Unknown resource: {uri}")
+    return f"contents of {name}"