Chat completion 401 when no Authorization header

When we send a request to `/api/chat/completions` without the `Authorization` header, the server just crashes and creates a stack trace, returning "Internal Server Error" to the calling client. With this fix, the server sends a 401 to the client with the content `{"detail": "Not authenticated"}`.

backend/open_webui/main.py

@@ -761,10 +761,22 @@ class PipelineMiddleware(BaseHTTPMiddleware):
         # Parse string to JSON
         data = json.loads(body_str) if body_str else {}
 
+        try:
             user = get_current_user(
                 request,
                 get_http_authorization_cred(request.headers["Authorization"]),
             )
+        except KeyError as e:
+            if len(e.args) > 1:
+                return JSONResponse(
+                    status_code=e.args[0],
+                    content={"detail": e.args[1]},
+                )
+            else:
+                return JSONResponse(
+                    status_code=status.HTTP_401_UNAUTHORIZED,
+                    content={"detail": "Not authenticated"},
+                )
 
         try:
             data = filter_pipeline(data, user)