iOS Google Sign In and Authenticating Token on Python Backend Not Working

Question

On my backend, I am trying to extract credentials from the auth_code returned after the I successfully signs in using google on my iphone Simulator using the below code:

credentials = client.credentials_from_clientsecrets_and_code(
        CLIENT_SECRET_FILE,
        ['https://www.googleapis.com/auth/calendar.readonly'],
        auth_code,
    )

The auth code is obtained fusing GIDSignIn on iOS and passed to my Python FastAPI server to call the code above on it. But I'm constantly getting a request_uri_mismatch error:

oauth2client.client.FlowExchangeError: redirect_uri_mismatchBad Request

I know client is a deprecated library, but I also tried the newer google-auth libraries and they use Flow and return the same error too.

I've followed and re-checked Google's tutorial here extensively: https://developers.google.com/identity/sign-in/ios/offline-access. I've also referred to the other Stack Overflow answers and extensively checked my enabled redirect urls , but it still does not work for some reason

What does work though is that I tried verifying the ID Token and that works fine and properly returns the email and user properties

verified_info = id_token_verifier.verify_oauth2_token(id_token, requests.Request(), CLIENT_ID)

I use client credentials for iOS and backend credentials and here are my credentials:

Backend:

iOS:

Answer 1

After scrolling through dozens of other answers, finally I found a gentleman's suggestion to simply add redirect_uri='' like so:

    credentials = client.credentials_from_clientsecrets_and_code(
        CLIENT_SECRET_FILE,
        ['https://www.googleapis.com/auth/calendar.readonly'],
        auth_code,
        redirect_uri=""
    )