Example Sign In activity for Google Sign-In on Android that retrieves an authorization code for use with server side authentication. See http://www.riskcompletefailure.com/2016/07/server-side-google-api-access-from.html for more background and links.

gistfile1.java

package com.example.anothersignintest;

import com.google.android.gms.auth.api.Auth;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
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;
import com.google.android.gms.common.api.OptionalPendingResult;
import com.google.android.gms.common.api.ResultCallback;
import com.google.android.gms.common.api.Status;

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

public class SignInTestActivity extends AppCompatActivity implements
        GoogleApiClient.OnConnectionFailedListener, OnClickListener {

    private static final String TAG = "SignInTestActivity";

    // A magic number we will use to know that our sign-in error
    // resolution activity has completed.
    private static final int OUR_REQUEST_CODE = 49404;

    // The core Google Play Services client.
    private GoogleApiClient mGoogleApiClient;

    // A progress dialog to display when the user is connecting in
    // case there is a delay in any of the dialogs being ready.
    private ProgressDialog mConnectionProgressDialog;

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

        // First we need to configure the Google Sign In API to ensure we are retrieving
        // the server authentication code as well as authenticating the client locally.
        String serverClientId = getString(R.string.server_client_id);
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestServerAuthCode(serverClientId)
                .requestEmail()
                .build();

        // We pass through three "this" arguments to the builder, specifying the:
        // 1. Context
        // 2. Object to use for resolving connection errors
        // 3. Object to call onConnectionFailed on
        // We also add the Google Sign in API we previously created.
        mGoogleApiClient = new GoogleApiClient.Builder(this /* Context */)
                .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
                .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
                .build();

        // Connect our sign in, sign out and disconnect buttons.
        findViewById(R.id.sign_in_button).setOnClickListener(this);
        findViewById(R.id.sign_out_button).setOnClickListener(this);
        findViewById(R.id.revoke_access_button).setOnClickListener(this);
        findViewById(R.id.sign_out_button).setVisibility(View.INVISIBLE);
        findViewById(R.id.revoke_access_button).setVisibility(View.INVISIBLE);

        // Configure the ProgressDialog that will be shown if there is a
        // delay in presenting the user with the next sign in step.
        mConnectionProgressDialog = new ProgressDialog(this);
        mConnectionProgressDialog.setMessage("Signing in...");
    }

    @Override
    public void onStart() {
        super.onStart();

        OptionalPendingResult<GoogleSignInResult> opr = Auth.GoogleSignInApi.silentSignIn(mGoogleApiClient);
        if (opr.isDone()) {
            // If the user's cached credentials are valid, the OptionalPendingResult will be "done"
            // and the GoogleSignInResult will be available instantly. We can try and retrieve an
            // authentication code.
            Log.d(TAG, "Got cached sign-in");
            GoogleSignInResult result = opr.get();
            handleSignInResult(result);
        } else {
            // If the user has not previously signed in on this device or the sign-in has expired,
            // this asynchronous branch will attempt to sign in the user silently.  Cross-device
            // single sign-on will occur in this branch.
            final ProgressDialog progressDialog = new ProgressDialog(this);
            progressDialog.setMessage("Checking sign in state...");
            progressDialog.show();
            opr.setResultCallback(new ResultCallback<GoogleSignInResult>() {
                @Override
                public void onResult(@NonNull GoogleSignInResult googleSignInResult) {
                    progressDialog.dismiss();
                    handleSignInResult(googleSignInResult);
                }
            });
        }
    }

    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
        // When we get here in an automanager activity the error is likely not
        // resolvable - meaning Google Sign In and other Google APIs will be
        // unavailable.
        Log.d(TAG, "onConnectionFailed:" + connectionResult);
    }


    protected void onActivityResult(int requestCode, int responseCode,
                                    Intent intent) {
        super.onActivityResult(requestCode, responseCode, intent);
        Log.v(TAG, "ActivityResult: " + requestCode);

        if (requestCode == OUR_REQUEST_CODE) {
            // Hide the progress dialog if its showing.
            mConnectionProgressDialog.dismiss();

            // Resolve the intent into a GoogleSignInResult we can process.
            GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(intent);
            handleSignInResult(result);
        }
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.sign_in_button:
                Log.v(TAG, "Tapped sign in");
                // Show the dialog as we are now signing in.
                mConnectionProgressDialog.show();

                Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient);
                startActivityForResult(signInIntent, OUR_REQUEST_CODE);
                break;
            case R.id.sign_out_button:
                Log.v(TAG, "Tapped sign out");
                // This will clear the default account in order to allow the user
                // to potentially choose a different account from the
                // account chooser.
                Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(
                        new ResultCallback<Status>() {
                            @Override
                            public void onResult(@NonNull Status status) {
                                // Hide the sign out buttons, show the sign in button.
                                findViewById(R.id.sign_in_button).setVisibility(View.VISIBLE);
                                findViewById(R.id.sign_out_button)
                                        .setVisibility(View.INVISIBLE);
                                findViewById(R.id.revoke_access_button).setVisibility(
                                        View.INVISIBLE);
                            }
                        });
                break;
            case R.id.revoke_access_button:
                Log.v(TAG, "Tapped disconnect");
                // Go away and revoke access to this entire application.
                Auth.GoogleSignInApi.revokeAccess(mGoogleApiClient).setResultCallback(
                        new ResultCallback<Status>() {
                            @Override
                            public void onResult(@NonNull Status status) {
                                // The GoogleApiClient is now disconnected and access has been
                                // revoked. We should now delete any data we need to comply with
                                // the developer properties.

                                // Hide the sign out buttons, show the sign in button.
                                findViewById(R.id.sign_in_button).setVisibility(View.VISIBLE);
                                findViewById(R.id.sign_out_button).setVisibility(View.INVISIBLE);
                                findViewById(R.id.revoke_access_button).setVisibility(View.INVISIBLE);
                            }
                        });
                break;
            default:
                // Unknown id.
                Log.v(TAG, "Unknown button press");
        }
    }

    /**
     * Helper method to trigger retrieving the server auth code if we've signed in.
     */
    private void handleSignInResult(GoogleSignInResult result ) {
        if (result.isSuccess()) {
            GoogleSignInAccount acct = result.getSignInAccount();
            // If you don't already have a server session, you can now send this code to your
            // server to authenticate on the backend.
            String authCode = acct.getServerAuthCode();

            // Hide the sign in buttons, show the sign out button.
            findViewById(R.id.sign_in_button).setVisibility(View.INVISIBLE);
            findViewById(R.id.sign_out_button)
                    .setVisibility(View.VISIBLE);
            findViewById(R.id.revoke_access_button).setVisibility(
                    View.VISIBLE);
        }
    }
}

Can I use this base for Google+ login in my application?

Hi Ian,
I am trying to use your example for my app, but in my logcat an error occurs like "This application may be doing too much work in its main thread". App can't pass after "Signing in" message. I googled it but actually I can't find any solution. Do you have any idea?

hey Ian
i am trying to use your example for my app.
when i run the app i got this type or error " error opening trace file: No such file or directory (2)"
plz help me

Awesome example

On first signup how do you handle repeated UserRecoverableAuthException

Hi , Mr kalidas the website holder of github, am unable to see the complete code as like before , ex- src folder, main activity , manifest file an all folders separately . have this site has done any modifications , even i hv to make an account for this site ., but earlier it was not so , it was easy to access it , now pls help me for receiving codes or accesing this site.

please reply on my email richason023@gmail.com

I want to navigate from LoginScreen activity to the MainActivity once its done. Can you assist me on how its done. Comments in the above code came in handy!
Cheers! @ianbarbe

WANT TO LOGOUT FROM OTHER ACTIVITY i.e from Navigation Drawer ,
mGoogleApiClient is null always

Hi @ianbarber, I have other activity who do Sign Out, so How to do that? Means I have to pass mGoogleApiClient object to other activity, can you please suggest me the best way to do that ?