Firebase Auth for Dart

pub package

A pure Dart implementation for Firebase Auth, which helps you authenticate users using multiple methods and providers. This package is used by the Firebase Auth Desktop plugin.

Getting Started

This package can be used with pure Dart apps, so if you are aiming to use Firebase for your Flutter app, please use firebase_auth for iOS, Android, macOS and Web, and add firebase_auth_desktop for Linux and Windows.

First, please make sure you initialize Firebase for Dart by following the guide to install firebase_core.

  1. On the root of your project, run the following command:

    dart pub add firebase_auth_dart

  2. Import it:

    import 'package:firebase_auth_dart/firebase_auth_dart.dart';

Usage

Initialize the package by calling the API entry point:

FirebaseAuth auth = FirebaseAuth.instance;

By default, this allows you to interact with Firebase Auth using the default Firebase App used whilst installing Firebase. If however you'd like to use a secondary Firebase App, use the instanceFor method:

FirebaseApp secondaryApp = Firebase.app('SecondaryApp');
FirebaseAuth auth = FirebaseAuth.instanceFor(app: secondaryApp);

Authentication state

You can listen to changes in authentication states through the following streams:

  1. authStateChanges(): fires event upon changes in User state, on sign in and sign out.
 FirebaseAuth.instance
  .authStateChanges()
  .listen((User? user) {
    if (user == null) {
      print('User is currently signed out!');
    } else {
      print('User is signed in!');
    }
  });
  1. idTokenChanges(): in addition to listening to the changes in User state, it also fires events when the current user's token changes.
   FirebaseAuth.instance
  .idTokenChanges()
  .listen((User? user) {
    if (user == null) {
      print('User is currently signed out!');
    } else {
      print('User is signed in!');
    }
  });

Sign-in methods

Anonymous sign-in

To sign-in a user anonymously, call the signInAnonymously() method on the FirebaseAuth instance:

UserCredential userCredential = await FirebaseAuth.instance.signInAnonymously();

The user will persist across sessions, such as restarting the app, until the user explicitly signs out, or delete the app and its cache.

Email/Password Registration & Sign-in

  1. Registration: 
     try {
   UserCredential userCredential = await FirebaseAuth.instance.createUserWithEmailAndPassword(
     email: "barry.allen@example.com",
     password: "SuperSecretPassword!"
   );
 } on FirebaseAuthException catch (e) {
   if (e.code == 'weak-password') {
     print('The password provided is too weak.');
   } else if (e.code == 'email-already-in-use') {
     print('The account already exists for that email.');
   }
 } catch (e) {
   print(e);
 }
  2. Sign-in: 
     try {
   UserCredential userCredential = await FirebaseAuth.instance.signInWithEmailAndPassword(
     email: "barry.allen@example.com",
     password: "SuperSecretPassword!"
   );
 } on FirebaseAuthException catch (e) {
   if (e.code == 'weak-password') {
     print('The password provided is too weak.');
   } else if (e.code == 'email-already-in-use') {
     print('The account already exists for that email.');
   }
 } catch (e) {
   print(e);
 }

OAuth providers

The package supports OAuth sign-in providers such as Google, through signInWithCredential() method. This method takes a AuthCredential object, which requires the providerId and signInMethod.

However, to authenticate via an OAuth provider, you will need some kind of token returned after the user signs in with the provider to be passed to signInWithCredential(), mostly it means using another package to carry this flow for you. Currently, there's no package for any provider that is Dart only and not dependent on the Flutter SDK.

Phone Auth

To authenticate users using phone number, you need to enable Phone as a sign-in provider in Firebase Console for your project. Once enabled, trigger the auth flow by calling signInWithPhoneNumber method.

// Wait for the user to complete the reCAPTCHA & for an SMS code to be sent.
ConfirmationResult confirmationResult = await FirebaseAuth.instance.signInWithPhoneNumber('+44 7123 123 456');

This method will open the default browser of the user for reCAPTCHA verification. Once complete, you can then sign the user in by providing the SMS code to the confirm method on the resolved ConfirmationResult response:

UserCredential userCredential = await confirmationResult.confirm('123456');

Signing Out

To sign a user out, call the signOut() method:

await FirebaseAuth.instance.signOut();

If you are listening to changes in authentication state, a new event will be sent to your listeners.

User management

Once authenticated, you have access to the user via the User class. The class stores the current information about the user such as their unique user ID, any linked provider accounts and methods to manage the user.

The User class is returned from any authentication state listeners, or as part of a UserCredential when using authentication methods. If you are sure the user is currently signed-in, you can also access the User via the currentUser property on the FirebaseAuth instance. The examples below show how to access the user:

  1. Via currentUser:

    var currentUser = FirebaseAuth.instance.currentUser;

if (currentUser != null) {
  print(currentUser.uid);
}

  2. Via Sign-in methods:

    UserCredential userCredential = await FirebaseAuth.instance.signInAnonymously();

print(userCredential.user!.uid);

  3. Via state listener stream:

    FirebaseAuth.instance
  .authStateChanges()
  .listen((User? user) {
    if (user != null) {
      print(user.uid);
    }
  });

Deleting a user

If your user wishes to delete their account from your project, this can be achieved with the delete() method. Since this is a security-sensitive operation, it requires that user must have recently signed-in. You can handle this scenario by catching the error, for example:

try {
  await FirebaseAuth.instance.currentUser!.delete();
} on FirebaseAuthException catch (e) {
  if (e.code == 'requires-recent-login') {
    print('The user must reauthenticate before this operation can be executed.');
  }
}

Reauthenticating a user

As mentioned above, some operations such as deleting the user, updating their email address or providers require the user to have recently signed in. Rather than signing the user out and back in again, the reauthenticateWithCredential() method can be called. If a recent login is required, create a new AuthCredential and pass it to the method. For example, to reauthenticate with email & password, create a new EmailAuthCredential:

// Prompt the user to enter their email and password
String email = 'barry.allen@example.com';
String password = 'SuperSecretPassword!';

// Create a credential
AuthCredential credential = EmailAuthProvider.credential(email: email, password: password);

// Reauthenticate
await FirebaseAuth.instance.currentUser!.reauthenticateWithCredential(credential);

Emulator Usage

If you are using the local Authentication emulator, then it is possible to connect to this using the useAuthEmulator method. Ensure you pass the correct port on which the Firebase emulator is running on. Ensure you have enabled network connections to the emulators in your apps following the emulator usage instructions in the general FlutterFire installation notes for each operating system.

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  // Ideal time to initialize
  await FirebaseAuth.instance.useAuthEmulator('localhost', 9099);
  //...
}

Issue and Feedback

Please file any issues, bugs, or feature requests in our issue tracker.

To contribute a change to this plugin, please review our contribution guide and open a pull request.

Libraries

firebase_auth_dart
Support for Firebase authentication methods with pure dart implmentation.