Atlas App Services provides many authentication providers to log users into your app. Each provider creates a unique user identity. App Services and the Realm Swift SDK lets you merge multiple credentials into one user identity.
Consider an application that offers anonymous login. This allows users to explore the app without registering. If users like the application, they create permanent accounts. They sign up with SSO or email/password authentication. By default, this creates a new User object. The app must link the new identity with the original User.
You can link identities using linkUser(credentials:Credentials). This links authentication providers to a logged-in User object.
@interface LinkIdentitiesExample : NSObject@end@implementation LinkIdentitiesExample { RLMApp *app; RLMUser *anonymousUser;}- (void)runExample { app = [RLMApp appWithId:YOUR_APP_ID]; [self logInAnonymously];}- (void)logInAnonymously { [app loginWithCredential:[RLMCredentials anonymousCredentials] completion:^(RLMUser *user, NSError *error) { if (error != nil) { NSLog(@"Failed to log in: %@", [error localizedDescription]); return; } [self registerNewAccountAsAnonymousUser: user]; }];}- (void)registerNewAccountAsAnonymousUser:(RLMUser *)user { NSString *email = @"link2@example.com"; NSString *password = @"ganondorf"; [[app emailPasswordAuth] registerUserWithEmail:email password:password completion:^(NSError *error) { if (error != nil) { NSLog(@"Failed to register new account: %@", [error localizedDescription]); return; } [self linkUser:self->anonymousUser withCredentials:[RLMCredentials credentialsWithEmail:email password:password]]; }];}- (void)linkUser:(RLMUser *)user withCredentials:(RLMCredentials *)credentials { [[app currentUser] linkUserWithCredentials:credentials completion:^(RLMUser *user, NSError *error) { if (error != nil) { NSLog(@"Failed to link user: %@", [error localizedDescription]); return; } NSLog(@"Successfully linked user: %@", user); }];}@end let app = App(id: YOUR_APP_SERVICES_APP_ID)func logInAnonymously() { app.login(credentials: Credentials.anonymous) { (result) in switch result { case .failure(let error): print("Failed to log in: \(error.localizedDescription)") case .success(let user): registerNewAccount(anonymousUser: user) } }}func registerNewAccount(anonymousUser: User) { let email = "swift-link@example.com" let password = "ganondorf" app.emailPasswordAuth.registerUser(email: email, password: password) { (error) in guard error == nil else { print("Failed to register new account: \(error!.localizedDescription)") return } link(user: anonymousUser, with: Credentials.emailPassword(email: email, password: password)) }}func link(user: User, with credentials: Credentials) { user.linkUser(credentials: credentials) { (result) in switch result { case .failure(let error): print("Failed to link user: \(error.localizedDescription)") case .success(let user): print("Successfully linked user: \(user)") } }}logInAnonymously()New in version 10.16.0.
The Realm Swift SDK provides an async/await version of User.linkUser.
let app = App(id: YOUR_APP_SERVICES_APP_ID)func logInAnonymously() async throws -> User { let anonymousUser = try await app.login(credentials: Credentials.anonymous) let newAccountLinkedUser = try await registerNewAccount(anonymousUser: anonymousUser) return newAccountLinkedUser}func registerNewAccount(anonymousUser: User) async throws -> User { let email = "swift-async-link@example.com" let password = "ganondorf" try await app.emailPasswordAuth.registerUser(email: email, password: password) let linkedUser = try await link(user: anonymousUser, with: Credentials.emailPassword(email: email, password: password)) return linkedUser}func link(user: User, with credentials: Credentials) async throws -> User { try await user.linkUser(credentials: credentials)}do { let linkedUser = try await logInAnonymously() print("Successfully linked user async: \(linkedUser)")} catch { print("Failed to link user: \(error.localizedDescription)")}Starting with Realm Swift SDK Versions 10.15.0 and 10.16.0, many of the Realm APIs support the Swift async/await syntax. Projects must meet these requirements:
Swift SDK Version
Swift Version Requirement
Supported OS
10.25.0
Swift 5.6
iOS 13.x
10.15.0 or 10.16.0
Swift 5.5
iOS 15.x
If your app accesses Realm in an async/await context, mark the code with @MainActor to avoid threading-related crashes.
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