I am using Firebase Auth in my app to authenticate user using Google as the Identity Provider. Instead of just authentication, I also add an optional scope so that a user can authorize my app to access his Google Drive as well in one single step during the sign in process. In return, I can use Firebase SDK to retrieve the OAuth Access Token from Google which I can use to access the user's Google drive with no problem.
Question: Since access token is short-lived, how can I obtain the Google (NOT Firebase) refresh token so that I can renew the access token in case it expires? This token will be stored in the backend so that we can process some background updates even when the user is not actively using the app. I believe Firebase should have hold this refresh token somewhere so that it can refresh for me. I just need to get a hold of that so that I can do renew the access token using my own code. But I am not sure where is that located.