Mobile app using Firebase or Cloud Endpoints authentication with Google App Engine backend

[User C]

I am developing a Mobile app (Ionic) with the backend in Google App Engine (Python). This app needs to login using Google authentication and security interchange with Google App Engine (Python) application.

Google is showing 2 configurations to achieve this.

1. Mobile Client <-> Firebase <-> Google App Engine:

2. Mobile Client <-> Cloud Endpoints <-> App Engine:

In my current approach 1, the Ionic app is able to login to Google and exchange information with Firebase, Firebase is able to interact with Google App Engine, but I'm not sure how to get Ionic app to authentication and security interchange with Google App Engine.

Can I use this approach? 

OR do I need to use 2 Mobile Client <-> Cloud Endpoints <-> App Engine

Thank you.

[Renaud Tarnec]

Google has published last October a guide for authenticating users on App Engine using Firebase for Python
  https://cloud.google.com/appengine/docs/python/authenticating-users-firebase-appengine

[Alex (Cloud Platform Support)]

In fact your using the right approach as you also benefit from the Firebase infrastructure with the added functionalities as stated on its introductory page.

Now, the provided tutorial by Renaud is an excellent example of assembling an app according to your first configuration. You may want to look at the Authenticating users on the server section for more details on how your Ionic app would interact with the App Engine server. It is explained that once your users are signed-in via the added Firebase Authentication user interface (on your Ionic app), the communication between the app and the server is handled by tokens as described here.

The second approach is also possible, but you will have to implement your own authentication mechanism and use a similar application framework as Flask, which the provided tutorial application is already based on.