Authenticate with Firebase on iOS Using a Custom Authentication System

Before you begin

1. Add Firebase to your iOS project.
2. Include the following pods in your Podfile:

   pod 'Firebase/Auth'
   

3. Get your project's server keys:
   1. Go to the Credentials page of the Google API Console and select your project.
   2. Click Create credentials > Service account key. Select New service account, type any name, select JSON as the key type, and click Create.
   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 Firebase module:

   Objective-C

   @import Firebase;
   

   Swift

   import Firebase
   

2. Configure a FIRApp shared instance, typically in your application's application:didFinishLaunchingWithOptions: method:

   Objective-C

   // Use Firebase library to configure APIs
   [FIRApp configure];
   

   Swift

   // 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:

   Objective-C

   [[FIRAuth auth] signInWithCustomToken:customToken
                              completion:^(FIRUser *_Nullable user,
                                           NSError *_Nullable error) {
                                // ...
                              }];

   Swift

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

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, 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 Firebase 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:.

NSError *error;
[[FIRAuth auth] signOut:&error;];
if (!error) {
  // Sign-out succeeded
}

try! FIRAuth.auth()!.signOut()

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