[QUESTION] Raise exception in python-fastApi middleware

I am trying to validate token in fastapi middleware but this seems impossible. As i am thinking middleware needs to make next call although its not required. I am not able to find any good solution to handle token in one go in this python-fastapi backend. Any help is appreciated.

@app.middleware("http")
async def add_middleware_here(request: Request, call_next):
    token = request.headers["Authorization"]
    try:
        verification_of_token = verify_token(token)
        if verification_of_token:
            response = await call_next(request)
            return response
    except InvalidSignatureError as er:
        raise HTTPException(status_code=401)

My expectation is that it should throw 401 error once wrong token is provided. Instead it throws 500 with below Exception traceback:

Traceback (most recent call last):
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 385, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\uvicorn\middleware\proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\fastapi\applications.py", line 140, in __call__
    await super().__call__(scope, receive, send)
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\starlette\applications.py", line 134, in __call__
    await self.error_middleware(scope, receive, send)
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\starlette\middleware\errors.py", line 178, in __call__
    raise exc from None
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\starlette\middleware\errors.py", line 156, in __call__
    await self.app(scope, receive, _send)
  File "c:\users\covered\appdata\local\programs\python\python38\lib\site-packages\starlette\middleware\base.py", line 26, in __call__
    await response(scope, receive, send)
TypeError: 'NoneType' object is not callable

[chris-allnutt]

the comment in there has the solution tho return Response(content="", status_code=401)

but I agree this is unclear would be good to know if this should be in the documentation or if it’s a bug @tiangolo and others think should be addressed. Something like bubbling up if the caught below exception is already of type HTTPException.

[vancouverwill]

hey @priyankagupta34 I just came across the same issue, seems weirdly HTTPException doesn’t work in middle ware. See https://github.com/tiangolo/fastapi/issues/1125