gistfile1.txt

1. Attempt to perform the silent sign-in: 
    
    Task<GoogleSignInAccount> task = googleSignInClient.silentSignIn();

2. If step 1 succeeds, we can pass the GoogleSignInAccount to the Google Drive service.

3. If step 1 fails, prompt the user to sign in using:

    startActivityForResult(Utils.buildGoogleSignInClient().getSignInIntent(), ...)

By following this approach, the user only needs to sign in once to enable long-term data syncing with Google Drive.

To change their signed-in account, the user can simply call:

    Utils.buildGoogleSignInClient().signOut()

and repeat step 1.

Implementation of Utils.buildGoogleSignInClient()

    public static GoogleSignInClient buildGoogleSignInClient() {
        GoogleSignInOptions signInOptions =
                new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                        .requestIdToken(GOOGLE_DRIVE_CLIENT_ID)
                        .requestEmail()
                        .requestScopes(new Scope(DriveScopes.DRIVE_APPDATA))
                        .build();
        return GoogleSignIn.getClient(MyApplication.instance(), signInOptions);
    }

Passing GoogleSignInAccount to Google Drive Service (Step 2)

    private static Drive getDriveService(GoogleSignInAccount googleSignInAccount) {
        GoogleAccountCredential credential =
                GoogleAccountCredential.usingOAuth2(
                        MyApplication.instance(), Collections.singleton(DriveScopes.DRIVE_APPDATA)
                );

        credential.setSelectedAccount(googleSignInAccount.getAccount());
        Drive googleDriveService =
                new Drive.Builder(
                        AndroidHttp.newCompatibleTransport(),
                        new GsonFactory(),
                        credential)
                .setApplicationName(APPLICATION_NAME)
                .build();

        return googleDriveService;
    }