I have implemented Firebase Authentication in my app, using the Google Provider and the "https://www.googleapis.com/auth/drive.appdata" scope so my app can access its application folder within Google Drive
This part works fine and I retrieve the FireBaseUser once the authentication completes What I now want to do is to access my app storage on Google Drive, but I don't know how to do this using the result of the current authentication
I tried to follow this: https://github.com/gsuitedevs/java-samples/blob/master/drive/quickstart/src/main/java/DriveQuickstart.java
But this doesn't work on Android. The main issue is how to create the Credentials object Do you have any idea on how to initialize a Drive.Builder instance so I can write/read to the app Google Drive folder?
Thanks
This cannot be done directly, because the Firebase & Google login are not the same, even when having logged in to Firebase with a Google account. On Android one meanwhile only has the "last logged in Google account" available for the user's Drive (the one on the device, which has nothing to do with Firebase Authentication, where Google may only be used as an "Authentication Provider").
So there are generally two options available to you:
Grant a GCP service-account access to Drive API and use Cloud Functions to access it.
Instead use Cloud Storage, which is within the Firebase eco-system and is similar to Drive.
I could also think of a combined solution approach, where users would use Cloud Storage (together with Firebase Authentication) and having a Cloud Function which uses a service-account, which eg. copies or moves uploaded files into a folder your Drive.
Concerning that (obviously server-side) Java example, the credentials.json clearly hints for a service account... and this is exactly where you can obtain this file from. However, for Android this is pretty useless - because it has major security implications, to package service-account credentials in an easy to de-compile package and distribute it on the WWW (to everybody). The Google Play Store likely would not permit you to publish or even upload that, because there are security checks in place. You could in best case only deploy that code as App Engine module, but not as an Android module.
Sorry for having destroyed your delusions and for not being able to provide a ready-made solution for 500 imaginary internet points, which pay nothing - but at least I can tell what is technically possible and what isn't - which effectively might save you lots of time, trying to accomplish the impossible.