26.3. Firebase Authentication in Flutter: User Authentication with Email and Password

Firebase Authentication is a user authentication service that can be easily integrated into Flutter, a mobile app development framework. This service allows users to authenticate to your application using a variety of methods, including email and password authentication. In this chapter, we will discuss how to implement Firebase authentication in Flutter to authenticate users with email and password.

To start, we need to add the Firebase dependency to our Flutter project. This can be done by adding the following line to the 'pubspec.yaml' file:

dependencies:
  flutter:
    sdk: flutter
  firebase_auth: ^0.18.0+1

After adding the dependency, run the command 'flutter pub get' in the terminal to install the package.

Next, we need to configure Firebase in our Flutter app. This involves creating a Firebase project, adding an Android app to the Firebase project, and getting the 'google-services.json' file to add to our Flutter project. This file contains the keys and identifiers needed to connect our app to Firebase.

After setting up Firebase, we can start implementing email and password authentication. First, we need to import the 'firebase_auth' package into our Dart file. This can be done by adding the following line at the beginning of the file:

import 'package:firebase_auth/firebase_auth.dart';

Next, we need to create an instance of FirebaseAuth:

final FirebaseAuth _auth = FirebaseAuth.instance;

This instance will be used to call Firebase authentication methods. To authenticate a user with email and password, we can use the 'signInWithEmailAndPassword' method. This method accepts two strings as arguments - the user's email and password - and returns a Future that resolves to a UserCredential object. The UserCredential object contains information about the authenticated user, such as their ID, email, and whether they verified their email.

Future signInWithEmailPassword(String email, String password) async {
  return await _auth.signInWithEmailAndPassword(email: email, password: password);
}

If authentication is successful, the user will be authenticated and will be able to access the application's functionalities. If authentication fails, an exception will be thrown and we can handle this exception to show an error message to the user.

We may also allow users to create a new account using their email and password. For that, we can use the 'createUserWithEmailAndPassword' method. This method works similarly to the 'signInWithEmailAndPassword' method, but instead of authenticating an existing user, it creates a new user with the given email and password.

Future signUpWithEmailPassword(String email, String password) async {
  return await _auth.createUserWithEmailAndPassword(email: email, password: password);
}

Firebase authentication in Flutter is a powerful and flexible way to authenticate users in your app. With email and password authentication, you can provide a familiar and secure authentication experience for your users. However, Firebase also supports other authentication methods such as phone authentication and authentication through third-party identity providers such as Google and Facebook. This allows you to offer multiple authentication options to your users, depending on their needs and preferences.

In summary, Firebase authentication in Flutter is an essential feature for any application that requires user authentication. With its easy integration and wide range of authentication methods, it can help improve your application's user experience and security.