• Go to Firebase and in your App Console page Go to Authentication and enable Google Login.
• Follow all Steps correctly as mentioned in firebase docs for google sign-in
• Add the given dependencies and sync gradle
• Add SHA-1 fingerprint to your project in Firebase console
• Add Google Sign in button in UI and Get reference for the same (Normal Button wont Work)
• Just copy paste everything from Documentation and try to solve all errors
• Copy Paste Configure Google Sign in code to onCreate() and fix imports
• Add the signIn() method and create an integer for the Auth as RC_SIGN_IN=1
• Create GoogleApiClient object that is used in the signIn() and reference as :

//Most important part for google sign in:

mGoogleApiClient=new GoogleApiClient.Builder(getApplicationContext()) .enableAutoManage(this, new GoogleApiClient.OnConnectionFailedListener() { @Override public void onConnectionFailed(@NonNull ConnectionResult connectionResult) { Toast.makeText(MainActivity.this, "Connection Error", Toast.LENGTH_LONG).show(); } }) .addApi(Auth.GOOGLE_SIGN_IN_API,gso)
.build();

• Now add onActivityResult Method and fix all errors

• Now add the firebaseAuthWithGoogle Method

• Add FirebaseAuthentication object mAuth and reference as mAuth=FirebaseAuth.getInstance();

• Add the TAG String to anything

• This completes Google Sign in, but to redirect to another page :

• Create the page with a logout button where redirection is done.

• Create an FirebaseAuth.AuthStateListener and reference as:

mAuthListener=new FirebaseAuth.AuthStateListener() { @Override public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) { if(firebaseAuth.getCurrentUser()!=null) { startActivity(new Intent(MainActivity.this,AccountActivity.class)); } } };

• Override onStart and add mAuth.addAuthStateListener(mAuthListener);
• In the Logout Activity add FirebaseAuth object and in the onClick of button add FirebaseAuthobject.signOut();
• To redirect after signing out add AuthStateListener as above and check currentuser == null
• Override onStart similarly.
• For getting all details of a user Just create a FirebaseUser object and reference it as:
  user=mAuth.getCurrentUser();
• All methods to fetch details for the user is now available.