public class GoogleSignOutActivity extends BaseActivityUtil {

    private static final String TAG = GoogleSignInActivity.class.getSimpleName();

    private FirebaseAuth mAuth;
    private GoogleApiClient mGoogleApiClient;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        showProgressDialog();

        // GoogleSignInOptions 개체 구성
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken(getString(R.string.google_client_id))
                .requestEmail()
                .build();

        // Build a GoogleApiClient with access to the Google Sign-In API and the options specified by gso.
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .enableAutoManage(this, new GoogleApiClient.OnConnectionFailedListener() {
                    @Override
                    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
                        DebugLog.logD(TAG, "Login fail");
                    }
                })
                .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
                .build();

        // initialize auth
        mAuth = FirebaseAuth.getInstance();

        signOut();
    }

    public void signOut() {

        mGoogleApiClient.connect();
        mGoogleApiClient.registerConnectionCallbacks(new GoogleApiClient.ConnectionCallbacks() {

            @Override
            public void onConnected(@Nullable Bundle bundle) {

                mAuth.signOut();
                if (mGoogleApiClient.isConnected()) {

                    Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(new ResultCallback<Status>() {

                        @Override
                        public void onResult(@NonNull Status status) {

                            if (status.isSuccess()) {

                                DebugLog.logD(TAG, "User Logged out");
                                setResult(ResultCode.SIGN_OUT_SUCCESS);

                            } else {

                                setResult(ResultCode.SIGN_OUT_FAIL);
                            }

                            hideProgressDialog();
                            finish();
                        }
                    });
                }
            }

            @Override
            public void onConnectionSuspended(int i) {

                DebugLog.logD(TAG, "Google API Client Connection Suspended");

                setResult(ResultCode.SIGN_OUT_FAIL);
                hideProgressDialog();

                finish();
            }
        });
    }
}