GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_GAMES_SIGN_IN)
                .requestServerAuthCode("MyCID")
                .build();

        mAuth = FirebaseAuth.getInstance();
        super.onCreate(savedInstanceState);
        final FirebaseAuth auth = FirebaseAuth.getInstance();
        AuthCredential credential = PlayGamesAuthProvider.getCredential("MyCID");
        auth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            currentUser = auth.getCurrentUser();
                        } else {
                            Toast.makeText(MainActivity.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                        }
                    }
                });
        if (currentUser == null) {
            cu = "NO UID";
        } else {
            cu = currentUser.getUid();
        }