AppEngine Firebase example broken

[chrisroat]

The problem is in using Firebase for handling user login in this tutorial step, which walks the user in creating code like in this GitHub directory when completed.

To reproduce the problem:

1. Create firebase project
2. Create firebase app
3. In Authentication -> Sign-in method, set up Google and Email auth
4. In Authentication -> Settings, add 127.0.0.1 as authorized domain
5. In Project Settings -> General, in SDK setup and configuration, copy js for app config
6. Set up the codelab code and launch the site:

    $ 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 

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)

[chrisroat]

For the email/password side of things, I found a workaround from another bug filed against the ui library -- turn off email enumeration protection.
firebase/firebaseui-web#1040