Authentication

Implement authentication flows on iOS using the AuthenticationServices framework, including Sign in with Apple, OAuth/third-party web auth, Password AutoFill, and biometric authentication.

Contents

• Sign in with Apple
• Credential Handling
• Credential State Checking
• Token Validation
• Existing Account Setup Flows
• ASWebAuthenticationSession (OAuth)
• Password AutoFill Credentials
• Biometric Authentication
• SwiftUI SignInWithAppleButton
• Common Mistakes
• Review Checklist
• References

Sign in with Apple

Add the "Sign in with Apple" capability in Xcode before using these APIs.

UIKit: ASAuthorizationController Setup

import AuthenticationServices

final class LoginViewController: UIViewController {
    func startSignInWithApple() {
        let provider = ASAuthorizationAppleIDProvider()
        let request = provider.createRequest()
        request.requestedScopes = [.fullName, .email]

        let controller = ASAuthorizationController(authorizationRequests: [request])
        controller.delegate = self
        controller.presentationContextProvider = self
        controller.performRequests()
    }
}

extension LoginViewController: ASAuthorizationControllerPresentationContextProviding {
    func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
        view.window!
    }
}

Delegate: Handling Success and Failure

extension LoginViewController: ASAuthorizationControllerDelegate {
    func authorizationController(
        controller: ASAuthorizationController,
        didCompleteWithAuthorization authorization: ASAuthorization
    ) {
        guard let credential = authorization.credential
            as? ASAuthorizationAppleIDCredential else { return }

        let userID = credential.user  // Stable, unique, per-team identifier
        let email = credential.email  // nil after first authorization
        let fullName = credential.fullName  // nil after first authorization
        let identityToken = credential.identityToken  // JWT for server validation
        let authCode = credential.authorizationCode  // Short-lived code for server exchange

        // Save userID to Keychain for credential state checks
        // See references/keychain-biometric.md for Keychain patterns
        saveUserID(userID)

        // Send identityToken and authCode to your server
        authenticateWithServer(identityToken: identityToken, authCode: authCode)
    }

    func authorizationController(
        controller: ASAuthorizationController,
        didCompleteWithError error: any Error
    ) {
        let authError = error as? ASAuthorizationError
        switch authError?.code {
        case .canceled:
            break  // User dismissed
        case .failed:
            showError("Authorization failed")
        case .invalidResponse:
            showError("Invalid response")
        case .notHandled:
            showError("Not handled")
        case .notInteractive:
            break  // Non-interactive request failed -- expected for silent checks
        default:
            showError("Unknown error")
        }
    }
}

Credential Handling

ASAuthorizationAppleIDCredential properties and their behavior:

Critical: email and fullName are provided ONLY on the first authorization. Cache them immediately during the initial sign-up flow. If the user later deletes and re-adds the app, these values will not be returned.

func handleCredential(_ credential: ASAuthorizationAppleIDCredential) {
    // Always persist the user identifier
    let userID = credential.user

    // Cache name and email IMMEDIATELY -- only available on first auth
    if let fullName = credential.fullName {
        let name = PersonNameComponentsFormatter().string(from: fullName)
        UserProfile.saveName(name)  // Persist to your backend
    }
    if let email = credential.email {
        UserProfile.saveEmail(email)  // Persist to your backend
    }
}

Credential State Checking

Check credential state on every app launch. The user may revoke access at any time via Settings > Apple Account > Sign-In & Security.

func checkCredentialState() async {
    let provider = ASAuthorizationAppleIDProvider()
    guard let userID = loadSavedUserID() else {
        showLoginScreen()
        return
    }

    do {
        let state = try await provider.credentialState(forUserID: userID)
        switch state {
        case .authorized:
            proceedToMainApp()
        case .revoked:
            // User revoked -- sign out and clear local data
            signOut()
            showLoginScreen()
        case .notFound:
            showLoginScreen()
        case .transferred:
            // App transferred to new team -- migrate user identifier
            migrateUser()
        @unknown default:
            showLoginScreen()
        }
    } catch {
        // Network error -- allow offline access or retry
        proceedToMainApp()
    }
}

Credential Revocation Notification

NotificationCenter.default.addObserver(
    forName: ASAuthorizationAppleIDProvider.credentialRevokedNotification,
    object: nil,
    queue: .main
) { _