Google oAuth 2.0 API Authentication Error: Error 400 - redirect_uri_mismatch (does not comply with policy) DJANGO APP

Question

I am trying to get my google authentication working on a Django app that is requesting Gmail and Calendar data. I have set up the oAuth API in the Google developer console and linked it with my project, and I've triple-checked that my redirect URI perfectly matches that in the code (No errors with HTTP vs. HTTPS nor any inconsistencies with the slashes). I made sure that my key, secret key, ClientID, and Client Secret are all configured and identical in my Django app's admin page. I have followed many youtube tutorials and searched other questions on stack overflow but Authentication is still not working. I am getting an Error 400: redirect_uri_mismatch. Even though I have checked many times to confirm that they are the same.

From all the tutorials, I have learned that there are two main origins for this error:

1. Server sided (can be fixed in the cloud hosting developer console)
2. Client sided (can be fixed by altering the code)

Both of these errors have their own individualized messages saying what type of mismatch it is.

Mine, however, says this: You can't sign in to this app because it doesn't comply with Google's OAuth 2.0 policy. \n\nIf you're the app developer, register the redirect URI in the Google Cloud Console.

Here is a photo of the Google Authentication error message

from django.shortcuts import render, redirect
from django.http import HttpRequest
from google_auth_oauthlib.flow import Flow
from google.auth.transport.requests import Request
from googleapiclient.discovery import build
from .models import CredentialsModel
from django.conf import settings
from django.core.exceptions import ObjectDoesNotExist
import os


os.environ['OAUTHLIB_INSECURE_TRANSPORT'] = '1'
os.environ['OAUTHLIB_RELAX_TOKEN_SCOPE'] = '1'
#Scopes are what we should be allowed to access
SCOPES = ['https://mail.google.com/', 'https://www.googleapis.com/auth/userinfo.email', 'https://www.googleapis.com/auth/userinfo.profile', 'openid']


"""
IF HAVING ISSUES WITH ANON USER:
Make sure you are on 127.0.0.1:8000, not localhost, both from the test-page and
the callback page. For some reason they are treated as different sessions and thus will have
issues maintaining a logged in user
"""

def oauth2callback(request):
    activeUser = request.user
    #URL is what we need to use for authentication
    authorization_response = request.build_absolute_uri()
    flow = Flow.from_client_secrets_file(
            settings.GOOGLE_OAUTH2_CLIENT_SECRETS_JSON,
            scopes=SCOPES,

            #This is where we are redirected after authentication
            redirect_uri='http://127.0.0.1:8000/google/oauth2callback')
    #Now get proper token
    flow.fetch_token(authorization_response = authorization_response)
    #print(request.user)
    #Now save in our database
    #print(flow.credentials)
    try :
        my_credential = CredentialsModel.objects.get(pk = activeUser)
    except ObjectDoesNotExist:
        CredentialsModel.objects.create(id = activeUser, credential = flow.credentials)
    else:
        my_credential.credential = flow.credentials
        my_credential.save()

    return redirect(flow.redirect_uri)     #activeUser.get_absolute_url())

Answer 1

google's documentation is not clear on this part (probably a bug on google's end too):

go to your GCP console, under OAuth consent screen, when the Publishing status is In production, we can still put http://localhost:8080/oauth-authorized/google under the Authorized redirect URIs without triggering the red error message saying Invalid Redirect. However, it doesn't work unless the app is in Testing status.

so in order to test your app at http://127.0.0.1:8000, you need to bring your GCP app to Testing status