AppEngine Firebase example broken

The problem is in using Firebase for handling user login in [this tutorial step](https://docs.cloud.google.com/appengine/docs/standard/python3/building-app/authenticating-users), which walks the user in creating code like in [this GitHub directory](https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/appengine/standard_python3/building-an-app/building-an-app-3) when completed. To reproduce the problem: 1. Create firebase project 1. Create firebase app 1. In Authentication -> Sign-in method, set up Google and Email auth 1. In Authentication -> Settings, add 127.0.0.1 as authorized domain 1. In Project Settings -> General, in SDK setup and configuration, copy js for app config 1. Set up the codelab code and launch the site: <pre><code> $ git clone https://github.com/GoogleCloudPlatform/python-docs-samples $ cd python-docs-samples/appengine/standard_python3/building-an-app/building-an-app-3 ## Update TODO in templates/index.html with app config js from above $ python3.13 -m venv .venv $ source .venv/bin/activate $ pip install -r requirements.txt $ python main.py </code></pre> The site can be viewed at http://127.0.0.1:8080/ Signing in with either of the two methods fails: - Sign in with Google: OAuth flow completes but user is not signed in when redirect back to site (user is not present in database) - Sign in with email: works first time, but cannot sign in again (user is present in database)