The sample (read: crude) implementation of the New Google Sign In API

GoogleSignInActivity.java

package com.horntell.pendulum;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

import com.google.android.gms.auth.api.Auth;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.auth.api.signin.GoogleSignInResult;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;

public class GoogleSignInActivity extends AppCompatActivity
        implements GoogleApiClient.OnConnectionFailedListener,
        View.OnClickListener {

    private static final String TAG = "NewGoogleSignInActivity";
    private static final int RC_SIGN_IN = 9001;
    private GoogleApiClient mGoogleApiClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_new_google_sign_in);

        // Configure sign-in to request the user's ID, email address, and basic
        // profile. ID and basic profile are included in DEFAULT_SIGN_IN.
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestEmail()
                .requestIdToken("463286871841-4cjcbqdihgqv8dlk6mm70v45a0l8usue.apps.googleusercontent.com")
                .build();

        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
                .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
                .build();

        findViewById(R.id.sign_in_button).setOnClickListener(this);

    }

    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
        Log.i(TAG, "onConnectionFailed: " + connectionResult.toString());
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.sign_in_button) {
            signIn();
        }
    }

    private void signIn() {
        Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient);
        startActivityForResult(signInIntent, RC_SIGN_IN);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
        if (requestCode == RC_SIGN_IN) {
            GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data);
            if(result.getSignInAccount() == null) {
                Log.i(TAG, "onActivityResult: RESULT: NULL");
            } else {
                Log.i(TAG, "onActivityResult: " + result.getStatus());
                Log.i(TAG, "onActivityResult: EMAIL: " + result.getSignInAccount().getEmail());
                Log.i(TAG, "onActivityResult: ID_TOKEN: " + result.getSignInAccount().getIdToken());
            }
        }
    }
}