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Authenticate with Firebase on Apple Platforms Using a Custom Authentication System

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You can integrate Firebase Authentication with a custom authentication system by modifying your authentication server to produce custom signed tokens when a user successfully signs in. Your app receives this token and uses it to authenticate with Firebase.

Before you begin

Use Swift Package Manager to install and manage Firebase dependencies.

  1. In Xcode, with your app project open, navigate to File > Add Packages.
  2. When prompted, add the Firebase Apple platforms SDK repository:
  4. Choose the Firebase Authentication library.
  5. When finished, Xcode will automatically begin resolving and downloading your dependencies in the background.

Next, perform some configuration steps:

  1. Get your project's server keys:
    1. Go to the Service Accounts page in your project's settings.
    2. Click Generate New Private Key at the bottom of the Firebase Admin SDK section of the Service Accounts page.
    3. The new service account's public/private key pair is automatically saved on your computer. Copy this file to your authentication server.

Authenticate with Firebase

  1. Import the FirebaseCore module in your UIApplicationDelegate, as well as any other Firebase modules your app delegate uses. For example, to use Cloud Firestore and Authentication:


    import FirebaseCore
    import FirebaseFirestore
    import FirebaseAuth
    // ...


    @import FirebaseCore;
    @import FirebaseFirestore;
    @import FirebaseAuth;
    // ...
  2. Configure a FirebaseApp shared instance in your app delegate's application(_:didFinishLaunchingWithOptions:) method:


    // Use Firebase library to configure APIs


    // Use Firebase library to configure APIs
    [FIRApp configure];
  3. When users sign in to your app, send their sign-in credentials (for example, their username and password) to your authentication server. Your server checks the credentials and returns a custom token if they are valid.
  4. After you receive the custom token from your authentication server, pass it to signInWithCustomToken to sign in the user:


    Auth.auth().signIn(withCustomToken: customToken ?? "") { user, error in
      // ...


    [[FIRAuth auth] signInWithCustomToken:customToken
                               completion:^(FIRAuthDataResult * _Nullable authResult,
                                            NSError * _Nullable error) {
      // ...

Next steps

After a user signs in for the first time, a new user account is created and linked to the credentials—that is, the user name and password, phone number, or auth provider information—the user signed in with. This new account is stored as part of your Firebase project, and can be used to identify a user across every app in your project, regardless of how the user signs in.

  • In your apps, you can get the user's basic profile information from the FIRUser object. See Manage Users.

  • In your Firebase Realtime Database and Cloud Storage Security Rules, you can get the signed-in user's unique user ID from the auth variable, and use it to control what data a user can access.

You can allow users to sign in to your app using multiple authentication providers by linking auth provider credentials to an existing user account.

To sign out a user, call signOut:.


    let firebaseAuth = Auth.auth()
do {
  try firebaseAuth.signOut()
} catch let signOutError as NSError {
  print("Error signing out: %@", signOutError)


    NSError *signOutError;
BOOL status = [[FIRAuth auth] signOut:&signOutError];
if (!status) {
  NSLog(@"Error signing out: %@", signOutError);

You may also want to add error handling code for the full range of authentication errors. See Handle Errors.