We have already discussed how to enable Firebase authentication using email and password in our Firebase Getting Started Tutorial

This tutorial is very important as now a days almost all apps have the option for Login with Google and Login with Facebook. This allows users to Sign-In to the app without requiring them to enter any email and password.
Although we have already discussed, how to implement Google Login in android app. Firebase Google Login goes a step forward and makes it very easy to implement Google based authentication.
Additionally, we can make use of all the features offered by Firebase, if we use Firebase Google Login.
In this tutorial, we will create a basic Android Firebase Login app which allows the user to Sign-In using Google and then display their name and email. So let’s get started.

Add Firebase Google Login for Authentication

To add Firebase Google Login follow the below steps :

1. Go to Firebase Website firebase.google.com and create a firebase account to start with. Go to Firebase console and Create a New Project by clicking on the “Create New Project” Button.
2. Give the Project name and country you are currently in, Once you are done click on “Create Project” button.
3. In the next screen choose “Add Firebase to your Android app” and then add the package details and Debug signing certificate SHA-1 key. Please note that adding SHA-1 key is mandatory for implementing google login. If you are not sure how to generate SHA-1 fingerprint see the following tutorial Adding Google Login to Android Apps under the heading Generate SHA-1 fingerprint


This will download the google-services.json file. Download it to your computer. We will add it to our android app later.

4. In the projects dashboard. Click on Auth Menu, then in the SIGN-IN METHOD click on Google and enable it.

Create Android Firebase Login App

Once you are done with adding , Let’s create the Android Application that will connect to Firebase for user authentication using Firebase Google Login

1. Go to File → New → New Project and enter your Application Name.
2. Enter company domain, this is used to uniquely identify your App’s package worldwide. Remember to use the same package name as used in the firebase console.
3. Choose project location and minimum SDK and on the next screen choose Empty Activity, since we would be adding most of the code Ourselves. Then Click on Next.
4. Choose an Activity Name. Make sure Generate Layout File check box is selected, Otherwise we have to generate it ourselves.Then click on Finish. We have used the Activity Name as SignInActivity since this will be the default screen when the user opens the app for the first time.

Gradle will configure your project and resolve the dependencies, Once it is complete proceed for next steps.

Add Permissions and Dependencies

1. After Gradle syncs the project, add the google-services.json file to your project’s app folder as shown below.
2. Since we need to connect to the Network add the Internet permission in AndroidManifest.xml file.

AndroidManifest.xml

3. Now open your project’s build.gradle from the project’s home directory and add the following dependency.

build.gradle

	classpath 'com.google.gms:google-services:3.0.0'

4. Next, open your app’s build.gradle from the and add the following at the end.

build.gradle

	apply plugin: 'com.google.gms.google-services'

5. Also add the following dependency in the dependency section.

    compile 'com.google.firebase:firebase-core:9.8.0'
    compile 'com.google.firebase:firebase-auth:9.8.0'
    compile 'com.google.android.gms:play-services-auth:9.8.0'

Adding Functionality

Open activity_signin.xml and add the following code. We have two text views, one for displaying the Name and another for dislaying the Email of the Logged in user.
Then we have the custom sign in button by google com.google.android.gms.common.SignInButton, We also have a sign out button to sign out the user.

        // Configure Google Sign In
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken(getString(R.string.default_web_client_id))
                .requestEmail()
                .build();

mGoogleApiClient = new GoogleApiClient.Builder(this)
                .enableAutoManage(this , new GoogleApiClient.OnConnectionFailedListener() {
                    @Override
                    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {

                    }
                } /* OnConnectionFailedListener */)
                .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
                .build();

   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.isSuccess()) {
                // Google Sign In was successful, authenticate with Firebase
                GoogleSignInAccount account = result.getSignInAccount();
                firebaseAuthWithGoogle(account);

            } else {
                // Google Sign In failed, update UI appropriately
                // ...
            }
        }
    }

All the steps above were similar to adding Google Login to android.

    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;

In the onCreate() method add the following AuthStateListener(). When the user is logged in we set make the google signin button invisible and then get the user details from the Firebase User object and display them on the screen.

        mAuth = FirebaseAuth.getInstance();
        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                signInButton.setVisibility(View.GONE);
                signOutButton.setVisibility(View.VISIBLE);
                if (user != null) {
                    // User is signed in
                    Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());
                    if(user.getDisplayName() != null)
                        nameTextView.setText("HI " + user.getDisplayName().toString());
                    emailTextView.setText(user.getEmail().toString());

                } else {
                    // User is signed out
                    Log.d(TAG, "onAuthStateChanged:signed_out");
                }
                // ...
            }
        };

            signInButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    signIn();
                }
            });
            signOutButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    FirebaseAuth.getInstance().signOut();
                    Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(
                            new ResultCallback() {
                                @Override
                                public void onResult(Status status) {
                                    signInButton.setVisibility(View.VISIBLE);
                                    signOutButton.setVisibility(View.GONE);
                                    emailTextView.setText(" ".toString());
                                    nameTextView.setText(" ".toString());
                                }
                            });
                }
                // ..
            });

  @Override
    public void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
    }

    @Override
    public void onStop() {
        super.onStop();
        if (mAuthListener != null) {
            mAuth.removeAuthStateListener(mAuthListener);
        }
    }

    private void firebaseAuthWithGoogle(GoogleSignInAccount acct) {
        Log.d(TAG, "firebaseAuthWithGoogle:" + acct.getId());

        AuthCredential credential = GoogleAuthProvider.getCredential(acct.getIdToken(), null);
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener() {
                    @Override
                    public void onComplete(@NonNull Task task) {
                        Log.d(TAG, "signInWithCredential:onComplete:" + task.isSuccessful());

                        // If sign in fails, display a message to the user. If sign in succeeds
                        // the auth state listener will be notified and logic to handle the
                        // signed in user can be handled in the listener.
                        if (!task.isSuccessful()) {
                            Log.w(TAG, "signInWithCredential", task.getException());
                            Toast.makeText(SignInActivity.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }