Google Signing using Firebase Authentication in Android

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.SignInButton;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;

public class MainActivity extends AppCompatActivity {
    // Initialize variables
    SignInButton btSignIn;
    GoogleSignInClient googleSignInClient;
    FirebaseAuth firebaseAuth;

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

        // Assign variable
        btSignIn = findViewById(R.id.bt_sign_in);

        // Initialize sign in options the client-id is copied form google-services.json file
        GoogleSignInOptions googleSignInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken("438431947620-ecpi41uk3dhhf4mv8g8q993k3vs49ltm.apps.googleusercontent.com")
                .requestEmail()
                .build();

        // Initialize sign in client
        googleSignInClient = GoogleSignIn.getClient(MainActivity.this, googleSignInOptions);

        btSignIn.setOnClickListener((View.OnClickListener) view -> {
            // Initialize sign in intent
            Intent intent = googleSignInClient.getSignInIntent();
            // Start activity for result
            startActivityForResult(intent, 100);
        });

        // Initialize firebase auth
        firebaseAuth = FirebaseAuth.getInstance();
        // Initialize firebase user
        FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();
        // Check condition
        if (firebaseUser != null) {
            // When user already sign in redirect to profile activity
            startActivity(new Intent(MainActivity.this, ProfileActivity.class).setFlags(Intent.FLAG_ACTIVITY_NEW_TASK));
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        // Check condition
        if (requestCode == 100) {
            // When request code is equal to 100 initialize task
            Task<GoogleSignInAccount> signInAccountTask = GoogleSignIn.getSignedInAccountFromIntent(data);
            // check condition
            if (signInAccountTask.isSuccessful()) {
                // When google sign in successful initialize string
                String s = "Google sign in successful";
                // Display Toast
                displayToast(s);
                // Initialize sign in account
                try {
                    // Initialize sign in account
                    GoogleSignInAccount googleSignInAccount = signInAccountTask.getResult(ApiException.class);
                    // Check condition
                    if (googleSignInAccount != null) {
                        // When sign in account is not equal to null initialize auth credential
                        AuthCredential authCredential = GoogleAuthProvider.getCredential(googleSignInAccount.getIdToken(), null);
                        // Check credential
                        firebaseAuth.signInWithCredential(authCredential).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                            @Override
                            public void onComplete(@NonNull Task<AuthResult> task) {
                                // Check condition
                                if (task.isSuccessful()) {
                                    // When task is successful redirect to profile activity display Toast
                                    startActivity(new Intent(MainActivity.this, ProfileActivity.class).setFlags(Intent.FLAG_ACTIVITY_NEW_TASK));
                                    displayToast("Firebase authentication successful");
                                } else {
                                    // When task is unsuccessful display Toast
                                    displayToast("Authentication Failed :" + task.getException().getMessage());
                                }
                            }
                        });
                    }
                } catch (ApiException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private void displayToast(String s) {
        Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();
    }
}

import android.os.Bundle;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import com.bumptech.glide.Glide;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import androidx.credentials.CredentialManager;
import androidx.credentials.SignOutRequest;

public class ProfileActivity extends AppCompatActivity {
    // Initialize variables
    private ImageView ivImage;
    private TextView tvName;
    private Button btLogout;
    private FirebaseAuth firebaseAuth;
    private CredentialManager credentialManager;

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

        // Assign variables
        ivImage = findViewById(R.id.iv_image);
        tvName = findViewById(R.id.tv_name);
        btLogout = findViewById(R.id.bt_logout);

        // Initialize Firebase Auth
        firebaseAuth = FirebaseAuth.getInstance();

        // Initialize Firebase user
        FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();

        // Check condition
        if (firebaseUser != null) {
            // When Firebase user is not null, set image and name
            Glide.with(this).load(firebaseUser.getPhotoUrl()).into(ivImage);
            tvName.setText(firebaseUser.getDisplayName());
        }

        // Initialize Credential Manager
        credentialManager = CredentialManager.create(this);

        btLogout.setOnClickListener(view -> {
            // Sign out using Credential Manager
            SignOutRequest signOutRequest = new SignOutRequest.Builder().build();
            credentialManager.signOut(signOutRequest)
                .addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task) {
                        if (task.isSuccessful()) {
                            // Sign out from Firebase
                            firebaseAuth.signOut();
                            // Display Toast
                            Toast.makeText(getApplicationContext(), "Logout successful", Toast.LENGTH_SHORT).show();
                            // Finish activity
                            finish();
                        } else {
                            // Handle failure
                            Toast.makeText(getApplicationContext(), "Logout failed", Toast.LENGTH_SHORT).show();
                        }
                    }
                });
        });
    }
}