Fix MCP server error -32602: Authorization header lost in background tasks

ex_app/lib/main.py

@@ -23,7 +23,7 @@
 
 from ex_app.lib.agent import react
 from ex_app.lib.logger import log
-from ex_app.lib.mcp_server import UserAuthMiddleware, ToolListMiddleware
+from ex_app.lib.mcp_server import UserAuthMiddleware, ToolListMiddleware, MCPAuthHeaderMiddleware
 from ex_app.lib.provider import provider
 from ex_app.lib.tools import get_categories
 
@@ -72,6 +72,7 @@ async def exapp_lifespan(app: FastAPI):
 
 APP = FastAPI(lifespan=lifespan)
 APP.add_middleware(AppAPIAuthMiddleware)  # set global AppAPI authentication middleware
+APP.add_middleware(MCPAuthHeaderMiddleware)  # captures Authorization into ContextVar for FastMCP tasks
 categories=get_categories()
 
 SETTINGS = SettingsForm(

ex_app/lib/mcp_server.py

@@ -3,6 +3,8 @@
 import time
 import asyncio
 import inspect
+import logging
+from contextvars import ContextVar
 from functools import wraps
 
 from fastmcp.server.dependencies import get_context
@@ -13,6 +15,42 @@
 from ex_app.lib.tools import get_tools
 import requests
 
+logger = logging.getLogger(__name__)
+
+# ContextVar to propagate the Authorization header into FastMCP background tasks.
+# asyncio.create_task() copies the current context snapshot at task-creation time,
+# so a ContextVar set before the task is spawned is visible inside it — even after
+# Starlette's request context has been torn down.
+_mcp_auth_header: ContextVar[str | None] = ContextVar("_mcp_auth_header", default=None)
+
+
+class MCPAuthHeaderMiddleware:
+	"""Pure-ASGI middleware that captures the Authorization header from every
+	HTTP request and stores it in a ContextVar.
+
+	Must be added to the outer FastAPI app (APP) so it runs before FastMCP takes
+	ownership of the request. Because asyncio copies the current context when
+	spawning tasks, the ContextVar value is available inside FastMCP's background-
+	task processing even after the original Starlette request context is gone.
+	"""
+
+	def __init__(self, app):
+		self.app = app
+
+	async def __call__(self, scope, receive, send):
+		if scope["type"] == "http":
+			headers = {k: v for k, v in scope.get("headers", [])}
+			raw_auth = headers.get(b"authorization", b"")
+			auth_value = raw_auth.decode("latin-1") if raw_auth else None
+			token = _mcp_auth_header.set(auth_value)
+			try:
+				await self.app(scope, receive, send)
+			finally:
+				_mcp_auth_header.reset(token)
+		else:
+			await self.app(scope, receive, send)
+
+
 def get_user(authorization_header: str, nc: AsyncNextcloudApp) -> str:
 	response = requests.get(
 		f"{nc.app_cfg.endpoint}/ocs/v2.php/cloud/user",
@@ -29,10 +67,23 @@ def get_user(authorization_header: str, nc: AsyncNextcloudApp) -> str:
 
 class UserAuthMiddleware(Middleware):
 	async def on_message(self, context: MiddlewareContext, call_next):
-		# Middleware stores user info in context state
-		authorization_header = context.fastmcp_context.request_context.request.headers.get("Authorization")
+		# 1. Primary path: read from ContextVar — always works, including inside
+		#    FastMCP background tasks where the Starlette request context is gone.
+		authorization_header = _mcp_auth_header.get()
+
+		# 2. Fallback: try the live request context (works for non-background paths
+		#    and keeps compatibility if the transport behaviour changes).
 		if authorization_header is None:
+			try:
+				authorization_header = (
+					context.fastmcp_context.request_context.request.headers.get("Authorization")
+				)
+			except Exception:
+				pass
+
+		if not authorization_header:
 			raise Exception("Authorization header is missing/invalid")
+
 		nc = AsyncNextcloudApp()
 		user = get_user(authorization_header, nc)
 		await nc.set_user(user)
@@ -53,8 +104,12 @@ async def on_message(
 			call_next: CallNext[mt.ListToolsRequest, list[Tool]],
 	) -> list[Tool]:
 		global LAST_MCP_TOOL_UPDATE
-		if LAST_MCP_TOOL_UPDATE + 60 < time.time():
-			safe, dangerous = await get_tools(context.fastmcp_context.get_state("nextcloud"))
+		nc = context.fastmcp_context.get_state("nextcloud")
+		# Guard: only refresh the tool list when auth succeeded (nc is set) and
+		# the cache has expired. Previously this would crash on every message
+		# type (including `initialize`) because nc was None after auth failures.
+		if nc is not None and LAST_MCP_TOOL_UPDATE + 60 < time.time():
+			safe, dangerous = await get_tools(nc)
 			tools = await self.mcp.get_tools()
 			if LAST_MCP_TOOL_UPDATE + 60 < time.time():
 				for tool in tools.keys():