26.8. Firebase Authentication in Flutter: Access Authorization

One of the most important aspects of application development is user authentication. Authentication is the process of verifying a user's identity before granting access to system resources. In the context of Flutter, one of the most efficient and secure ways to implement user authentication is through Firebase. In this module, we'll explore how to implement Firebase authentication in a Flutter app.

Firebase is Google's application development platform that provides a variety of services including hosting, real-time database, cloud storage, and more. One such service is Firebase Authentication, which provides an easy-to-use, secure, and scalable backend authentication solution for authenticating users in mobile and web apps.

To get started, you first need to add the Firebase Auth package to your Flutter project. This can be done by adding the following line to your project's 'pubspec.yaml' file:

dependencies:
  firebase_auth: ^0.18.1+1

Next, you need to configure Firebase in your Flutter app. This involves creating a Firebase project, registering your app in that project, and getting a configuration file (google-services.json for Android and GoogleService-Info.plist for iOS) that you need to add to your Flutter project.

Once Firebase is set up, you can start using Firebase Auth to authenticate users in your app. Firebase Auth supports multiple authentication methods, including email/password authentication, phone authentication, Google authentication, Facebook authentication, and more.

To authenticate a user with email and password, you can use the createUserWithEmailAndPassword() method to create a new user account and the signInWithEmailAndPassword() method to authenticate an existing user. See an example of how this can be done:

FirebaseAuth _auth = FirebaseAuth.instance;

Future registerUser(String email, String password) async {
  try {
    UserCredential userCredential = await _auth.createUserWithEmailAndPassword(
      email: email,
      password: password,
    );
    // User registered successfully
  } on FirebaseAuthException catch (e) {
    // Handle registration error
  }
}

Future loginUser(String email, String password) async {
  try {
    UserCredential userCredential = await _auth.signInWithEmailAndPassword(
      email: email,
      password: password,
    );
    // User signed in successfully
  } on FirebaseAuthException catch (e) {
    // Handle sign in error
  }
}

To authenticate a user with Google, you need to add the google_sign_in package to your project and configure OAuth 2.0 in the Firebase console. You can then use the signInWithCredential() method with a GoogleAuthProvider to authenticate the user. See an example of how this can be done:

GoogleSignIn _googleSignIn = GoogleSignIn();
FirebaseAuth _auth = FirebaseAuth.instance;

Future signInWithGoogle() async {
  try {
    GoogleSignInAccount googleUser = await _googleSignIn.signIn();
    GoogleSignInAuthentication googleAuth = await googleUser.authentication;
    final AuthCredential credential = GoogleAuthProvider.credential(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    UserCredential userCredential = await _auth.signInWithCredential(credential);
    // User signed in with Google successfully
  } on FirebaseAuthException catch (e) {
    // Handle sign in error
  }
}

In addition, Firebase Auth provides methods to manage the user's session, such as signOut() to end the user's session and currentUser() to get the currently authenticated user. It also supports multiple user authentication on the same device.

In summary, Firebase authentication in Flutter is an efficient and secure way to authenticate users in your application. It supports various authentication methods, including email/password authentication, phone authentication, Google authentication, Facebook authentication, and so on, and provides methods to manage the user's session. With Firebase Auth, you can focus on developing your app's features, leaving user authentication to Firebase.