security: v1.7.7 hardening release

- Add WEBHOOK_CLIENT_SECRET validation for Graph webhooks
- Add Redis-backed rate limiting (fetch/ask/write/default tiers)
- Validate LLM_BASE_URL to prevent SSRF (HTTPS only, block private IPs)
- Enforce non-wildcard CORS when AUTH_ENABLED=true
- Add Content-Security-Policy headers
- Fix audit middleware to use verified JWT claims via contextvars
- Cap bulk_tags updates to 10,000 documents
- Return generic error messages to clients (no internal detail leakage)
- Strict AlertCondition Pydantic model for alert rules
- Security warning on MCP stdio server startup
- Remove MongoDB/Redis host ports from docker-compose
- Remove mongo_query from /ask API response

backend/routes/webhooks.py

@@ -1,4 +1,5 @@
 import structlog
+from config import WEBHOOK_CLIENT_SECRET
 from fastapi import APIRouter, Request, Response
 
 router = APIRouter()
@@ -10,9 +11,12 @@ async def graph_webhook(request: Request):
     """
     Receive Microsoft Graph change notifications.
     Handles the validation handshake by echoing validationToken.
+    Validates clientState on notifications to prevent spoofing.
     """
     validation_token = request.query_params.get("validationToken")
     if validation_token:
+        # Microsoft sends validationToken as a query param during subscription creation.
+        # Echo it back as plain text to prove endpoint ownership.
         return Response(content=validation_token, media_type="text/plain")
 
     try:
@@ -21,12 +25,26 @@ async def graph_webhook(request: Request):
         logger.warning("Invalid webhook payload", error=str(exc))
         return Response(status_code=400)
 
-    for notification in body.get("value", []):
+    notifications = body.get("value", [])
+    if not isinstance(notifications, list):
+        logger.warning("Invalid webhook payload structure")
+        return Response(status_code=400)
+
+    for notification in notifications:
+        client_state = notification.get("clientState")
+        if WEBHOOK_CLIENT_SECRET and client_state != WEBHOOK_CLIENT_SECRET:
+            logger.warning(
+                "Graph webhook rejected: invalid clientState",
+                change_type=notification.get("changeType"),
+                resource=notification.get("resource"),
+            )
+            return Response(status_code=401)
+
         logger.info(
             "Received Graph notification",
             change_type=notification.get("changeType"),
             resource=notification.get("resource"),
-            client_state=notification.get("clientState"),
+            client_state=client_state,
         )
 
     return {"status": "accepted"}