v1.7.12: security hardening — CORS fix, security headers, fail-closed rate limiter, OpenAPI docs disabled by default, config auth privacy, webhook validation

backend/routes/webhooks.py

@@ -17,7 +17,15 @@ async def graph_webhook(request: Request):
     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")
+        # Validate to prevent content injection if endpoint is hit directly.
+        if len(validation_token) > 1024 or not validation_token.isascii():
+            logger.warning("Invalid validationToken rejected", length=len(validation_token))
+            return Response(status_code=400)
+        return Response(
+            content=validation_token,
+            media_type="text/plain",
+            headers={"X-Content-Type-Options": "nosniff"},
+        )
 
     try:
         body = await request.json()