Signing in users with Apple on iOS

This document shows you how to use Identity Platform to add Sign in with Apple to your iOS app.

Before you begin

Create an iOS app that uses Identity Platform.
Join the Apple Developer Program.

Configuring your app with Apple

On the Apple Developer site:

Enable the Sign In with Apple capability for your app.
If you use Identity Platform to send emails to your users, configure your project with Apple's private email relay service using the following email:
```
noreply@project-id.firebaseapp.com
```
You can also use a custom email template, if your app has one.

Complying with Apple's anonymized data requirements

Apple gives users the option of anonymizing their data, including their email address. Apple assigns users who select this option an obfuscated email address with the domain privaterelay.appleid.com.

Your app must comply with any applicable developer policies or terms from Apple regarding anonymized Apple IDs. This includes obtaining user consent before associating any personally identifying information (PII) with an anonymized Apple ID. Actions that involve PII include, but are not limited to:

Linking an email address to an anonymized Apple ID, or vice versa.
Linking a phone number to an anonymized Apple ID, or vice versa
Linking a non-anonymous social credential, such as Facebook or Google, to to anonymized Apple ID, or vice versa.

For more information, refer to the Apple Developer Program License Agreement for your Apple developer account.

Configuring Apple as a provider

To configure Apple as an identity provider:

Go to the Identity Providers page in the Google Cloud console.

Go to the Identity Providers page
Click Add A Provider.
Select Apple from the list.
Under Platform, select iOS.
Enter your app's Bundle ID.
Register your app's domains by clicking Add domain under Authorized Domains. For development purposes, localhost is already enabled by default.
Under Configure your application, click iOS. Copy the snippet into your app's code to initialize the Identity Platform client SDK.
Click Save.

Signing in users with the client SDK

Sign in the user and obtain an ID token using Apple's Authentication Services framework.
Generate a random string, known as a nonce, by calling SecRandomCopyBytes(_:_:_:).

The nonce is used to prevent replay attacks. You include the SHA-256 hash of your nonce in your authentication request, and Apple returns it, unmodified, in the response. Identity Platform then validates the response by comparing the original hash to the value returned by Apple.

Start Apple's sign-in flow, including the SHA-256 hash of the nonce you created in the previous step, and a delegate class to handle Apple's response:

Swift

import CryptoKit

// Unhashed nonce.
fileprivate var currentNonce: String?

@available(iOS 13, *)
func startSignInWithAppleFlow() {
  let nonce = randomNonceString()
  currentNonce = nonce
  let appleIDProvider = ASAuthorizationAppleIDProvider()
  let request = appleIDProvider.createRequest()
  request.requestedScopes = [.fullName, .email]
  request.nonce = sha256(nonce)

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

@available(iOS 13, *)
private func sha256(_ input: String) -> String {
  let inputData = Data(input.utf8)
  let hashedData = SHA256.hash(data: inputData)
  let hashString = hashedData.compactMap {
    return String(format: "%02x", $0)
  }.joined()

  return hashString
}

Objective-C

@import CommonCrypto;

- (void)startSignInWithAppleFlow {
  NSString *nonce = [self randomNonce:32];
  self.currentNonce = nonce;
  ASAuthorizationAppleIDProvider *appleIDProvider = [[ASAuthorizationAppleIDProvider alloc] init];
  ASAuthorizationAppleIDRequest *request = [appleIDProvider createRequest];
  request.requestedScopes = @[ASAuthorizationScopeFullName, ASAuthorizationScopeEmail];
  request.nonce = [self stringBySha256HashingString:nonce];

  ASAuthorizationController *authorizationController =
      [[ASAuthorizationController alloc] initWithAuthorizationRequests:@[request]];
  authorizationController.delegate = self;
  authorizationController.presentationContextProvider = self;
  [authorizationController performRequests];
}

- (NSString *)stringBySha256HashingString:(NSString *)input {
  const char *string = [input UTF8String];
  unsigned char result[CC_SHA256_DIGEST_LENGTH];
  CC_SHA256(string, (CC_LONG)strlen(string), result);

  NSMutableString *hashed = [NSMutableString stringWithCapacity:CC_SHA256_DIGEST_LENGTH * 2];
  for (NSInteger i = 0; i < CC_SHA256_DIGEST_LENGTH; i++) {
    [hashed appendFormat:@"%02x", result[i]];
  }
  return hashed;
}

Handle Apple's response in your implementation of ASAuthorizationControllerDelegate. If sign-in succeeds, use the ID token from Apple's response with the unhashed nonce to authenticate with Identity Platform:

Swift

@available(iOS 13.0, *)
extension MainViewController: ASAuthorizationControllerDelegate {

  func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
    if let appleIDCredential = authorization.credential as? ASAuthorizationAppleIDCredential {
      guard let nonce = currentNonce else {
        fatalError("Invalid state: A login callback was received, but no login request was sent.")
      }
      guard let appleIDToken = appleIDCredential.identityToken else {
        print("Unable to fetch identity token")
        return
      }
      guard let idTokenString = String(data: appleIDToken, encoding: .utf8) else {
        print("Unable to serialize token string from data: \(appleIDToken.debugDescription)")
        return
      }
      // Initialize a Firebase credential.
      let credential = OAuthProvider.credential(withProviderID: "apple.com",
                                                IDToken: idTokenString,
                                                rawNonce: nonce)
      // Sign in with Firebase.
      Auth.auth().signIn(with: credential) { (authResult, error) in
        if error {
          // Error. If error.code == .MissingOrInvalidNonce, make sure
          // you're sending the SHA256-hashed nonce as a hex string with
          // your request to Apple.
          print(error.localizedDescription)
          return
        }
        // User is signed in to Firebase with Apple.
        // ...
      }
    }
  }

  func authorizationController(controller: ASAuthorizationController, didCompleteWithError error: Error) {
    // Handle error.
    print("Sign in with Apple errored: \(error)")
  }
}

Objective-C

- (void)authorizationController:(ASAuthorizationController *)controller
  didCompleteWithAuthorization:(ASAuthorization *)authorization API_AVAILABLE(ios(13.0)) {
  if ([authorization.credential isKindOfClass:[ASAuthorizationAppleIDCredential class]]) {
    ASAuthorizationAppleIDCredential *appleIDCredential = authorization.credential;
    NSString *rawNonce = self.currentNonce;
    NSAssert(rawNonce != nil, @"Invalid state: A login callback was received, but no login request was sent.");

    if (appleIDCredential.identityToken == nil) {
      NSLog(@"Unable to fetch identity token.");
      return;
    }
    NSString *idToken = [[NSString alloc] initWithData:appleIDCredential.identityToken
                                              encoding:NSUTF8StringEncoding];
    if (idToken == nil) {
      NSLog(@"Unable to serialize id token from data: %@", appleIDCredential.identityToken);
    }
    // Initialize a Firebase credential.
    FIROAuthCredential *credential = [FIROAuthProvider credentialWithProviderID:@"apple.com"
                                                                        IDToken:idToken
                                                                       rawNonce:rawNonce];
    // Sign in with Firebase.
    [[FIRAuth auth] signInWithCredential:credential
                              completion:^(FIRAuthDataResult * _Nullable authResult,
                                           NSError * _Nullable error) {
      if (error != nil) {
        // Error. If error.code == FIRAuthErrorCodeMissingOrInvalidNonce,
        // make sure you're sending the SHA256-hashed nonce as a hex string
        // with your request to Apple.
        return;
      }
      // Sign-in succeeded!
    }];
  }
}

- (void)authorizationController:(ASAuthorizationController *)controller
           didCompleteWithError:(NSError *)error API_AVAILABLE(ios(13.0)) {
  NSLog(@"Sign in with Apple errored: %@", error);
}

Unlike many other identity providers, Apple does not provide a photo URL.

If a user chooses not to share their real email with your app, Apple provisions a unique email address for that user to share instead. This email takes the form xyz@privaterelay.appleid.com. If you configured the private email relay service, Apple forwards emails sent to the anonymized address to the user's real email address.

Apple only shares user information, such as display names, with apps the first time a user signs in. In most cases, Identity Platform stores this data, which lets you fetch it using firebase.auth().currentUser.displayName during future sessions. However, if you allowed users to sign into your app using Apple before integrating with Identity Platform, user information is not available.

User account deletion

Apple requires that iOS apps that support account creation must also let users initiate deletion of their account from within the app.

When deleting a user account, you must revoke the user's token before deleting the user's account, as well as all data you stored for them in Firestore, Cloud Storage, and Firebase Realtime Database. For more information, see Offering account deletion in your app in Apple's developer support documentation.

Since Identity Platform does not store user tokens when users are created with Apple sign-in, you must ask the user to sign in before revoking their token and deleting the account. Alternatively, to avoid asking the user to sign in again if a user is signed in with Apple sign-in, you can store the authorization code to reuse during token revocation.

To revoke a user's token and delete their account, run the following:

Swift

let user = Auth.auth().currentUser

// Check if the user has a token.
if let providerData = user?.providerData {
  for provider in providerData {
    guard let provider = provider as? FIRUserInfo else {
      continue
    }
    if provider.providerID() == "apple.com" {
      isAppleProviderLinked = true
    }
  }
}

// Re-authenticate the user and revoke their token
if isAppleProviderLinked {
  let request = appleIDRequest(withState: "revokeAppleTokenAndDeleteUser")
  let controller = ASAuthorizationController(authorizationRequests: [request])
  controller.delegate = self
  controller.presentationContextProvider = self
  controller.performRequests()
} else {
  // Usual user deletion
}

func authorizationController(
  controller: ASAuthorizationController,
  didCompleteWithAuthorization authorization: ASAuthorization
) {
  if authorization.credential is ASAuthorizationAppleIDCredential {
    let appleIDCredential = authorization.credential as? ASAuthorizationAppleIDCredential
    if authorization.credential is ASAuthorizationAppleIDCredential {
      if appleIDCredential.state == "signIn" {
        // Sign in with Firebase.
        // ...
      } else if appleIDCredential.state == "revokeAppleTokenAndDeleteUser" {
        // Revoke token with Firebase.
        Auth.auth().revokeTokenWithAuthorizationCode(code) { error in
          if error != nil {
            // Token revocation failed.
          } else {
            // Token revocation succeeded then delete user again.
            let user = Auth.auth().currentUser
            user?.delete { error in
              // ...
            }
          }

        }
      }
    }
  }
}

Objective-C

FIRUser *user = [FIRAuth auth].currentUser;

// Check if the user has a token.
BOOL isAppleProviderLinked = false;
for (id<FIRUserInfo> provider in user.providerData) {
  if ([[provider providerID] isEqual:@"apple.com"]) {
    isAppleProviderLinked = true;
  }
}

// Re-authenticate the user and revoke their token
if (isAppleProviderLinked) {
  if (@available(iOS 13, *)) {
    ASAuthorizationAppleIDRequest *request =
        [self appleIDRequestWithState:@"revokeAppleTokenAndDeleteUser"];
    ASAuthorizationController *controller = [[ASAuthorizationController alloc]
        initWithAuthorizationRequests:@[ request ]];
    controller.delegate = self;
    controller.presentationContextProvider = self;
    [controller performRequests];
  }
} else {
  // Usual user deletion
}

- (void)authorizationController:(ASAuthorizationController *)controller
    didCompleteWithAuthorization:(ASAuthorization *)authorization
    API_AVAILABLE(ios(13.0)) {
  if ([authorization.credential
          isKindOfClass:[ASAuthorizationAppleIDCredential class]]) {
    ASAuthorizationAppleIDCredential *appleIDCredential =
        authorization.credential;

    if ([appleIDCredential.state isEqualToString:@"signIn"]) {
      // Sign in with Firebase.
      // ...
    } else if ([appleIDCredential.state
                  isEqualToString:@"revokeAppleTokenAndDeleteUser"]) {
      // Revoke token with Firebase.
      NSString *code =
          [[NSString alloc] initWithData:appleIDCredential.authorizationCode
                                encoding:NSUTF8StringEncoding];
      [[FIRAuth auth]
          revokeTokenWithAuthorizationCode:code
                                completion:^(NSError *_Nullable error) {
                                  if (error != nil) {
                                    // Token revocation failed.
                                  } else {
                                    // Token revocation succeeded then delete
                                    // user again.
                                    FIRUser *user = [FIRAuth auth].currentUser;
                                    [user deleteWithCompletion:^(
                                              NSError *_Nullable error){
                                        // ...
                                    }];
                                  }
                                }];
    }
  }
}

What's next

Learn more about Identity Platform users.
Sign in users with other identity providers.