FastAPI – Unable to get auth token from middleware’s Request object

Following Starlette documentation (FastAPI uses Starlette for middlewares), response.headers["Authorization"] should allow me to get the bearer token, but I get a KeyError saying no such attribute exists.

When I print response.headers, I get MutableHeaders({'content-length': '14', 'content-type': 'application/json'}).

Why is the authorization attribute not in the header despite of making a request with an auth header?

@app.middleware("http")
async def validate_access_token(request: Request, call_next):
    response = await call_next(request)
    access_token = response.headers["Authorization"].split()
    is_valid_signature = jwt.decode(access_token[1], key=SECRET, algorithms=CRYPT_ALGO)
    
    if is_valid_signature:
        return response
    else:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED, 
            detail='Invalid access token'
        )

Answer

You are trying to retrieve the Authorization header from the Respone instead of the Request object (as you mentioned in the title of your question). Hence, you should instead use:

access_token = request.headers['Authorization']
               ^^^^^^^

or

access_token = request.headers.get('Authorization')

Additionally, instead of a middleware, it might be better to use Dependencies, along with FastAPI’s OAuth2PasswordBearer (you can find the implementation here), similar to this answer (which demonstrates how to achieve authentication using the third-party package FastAPI_Login – have a look at the relevant implementation here).