Login With Apple in Swift with Firebase

Login.swift

// Created by Yasushi Oh on 1/22/24.
// Referenced from ChatGPT
//UI View with the Login button component

import SwiftUI
import AuthenticationServices

struct Login: View {
    var body: some View {
        VStack {
            LoginWithApple()
                .frame(width: 280, height: 45)
                
        }
    }
}

#Preview {
    Login()
}

LoginWithApple.swift

// Created by Yasushi Oh on 1/22/24.
// Referenced from ChatGPT and Firebase Documentation https://firebase.google.com/docs/auth/ios/apple
// Login button component

import SwiftUI
import AuthenticationServices
import FirebaseAuth

struct LoginWithApple: UIViewRepresentable {
    func makeUIView(context: Context) -> ASAuthorizationAppleIDButton {
        let button = ASAuthorizationAppleIDButton()
        button.addTarget(context.coordinator, action: #selector(Coordinator.handleAuthorizationAppleIDButtonPress), for: .touchUpInside)
        return button
    }
    
    func updateUIView(_ uiView: ASAuthorizationAppleIDButton, context: Context) {
    }
    
    func makeCoordinator() -> Coordinator {
        return Coordinator()
    }
}

class Coordinator: NSObject, ASAuthorizationControllerDelegate {
    fileprivate var currentNonce: String?
    
    @objc func handleAuthorizationAppleIDButtonPress() {
        let nonce = UserAuth.randomNonceString()
        currentNonce = nonce
        let appleIDProvider = ASAuthorizationAppleIDProvider()
        let request = appleIDProvider.createRequest()
        request.requestedScopes = [.fullName, .email]
        request.nonce = UserAuth.sha256(nonce)
        let authorizationController = ASAuthorizationController(authorizationRequests: [request])
        authorizationController.delegate = self
        authorizationController.performRequests()
        }
    
    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, including the user's full name.
              let credential = OAuthProvider.appleCredential(withIDToken: idTokenString,
                                                                rawNonce: nonce,
                                                                fullName: appleIDCredential.fullName)
              // Sign in with Firebase.
              Auth.auth().signIn(with: credential) { (authResult, error) in
                  if (error != nil) {
                  // 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 ?? "Firebase cannot process the nonce")
                  return
                }
                // User is signed in to Firebase with Apple.
                //Please ignore warning, debug only, will remove in the future
                  print(authResult?.user.uid);
              }
            }
    }
    
    func authorizationController(controller: ASAuthorizationController, didCompleteWithError error: Error) {
        print("Sign in with Apple errored: \(error)")
    }
}



#Preview {
    LoginWithApple()
}

UserAuth.swift

// Created by Yasushi Oh on 1/22/24.
// Referenced from Firebase Documentation https://firebase.google.com/docs/auth/ios/apple
// Hash functions

import Foundation
import CryptoKit
import AuthenticationServices

public class UserAuth {
    public static func randomNonceString(length: Int = 32) -> String {
      precondition(length > 0)
      var randomBytes = [UInt8](repeating: 0, count: length)
      let errorCode = SecRandomCopyBytes(kSecRandomDefault, randomBytes.count, &randomBytes)
      if errorCode != errSecSuccess {
        fatalError(
          "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)"
        )
      }

      let charset: [Character] =
        Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")

      let nonce = randomBytes.map { byte in
        // Pick a random character from the set, wrapping around if needed.
        charset[Int(byte) % charset.count]
      }

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

      return hashString
    }

        
    
}

This is an out of the box solution for login with Apple using Firebase Auth. But it is not quite out of the box, make sure you:

1. Set up the Google Firebase settings and Apple settings following https://firebase.google.com/docs/auth/ios/apple
2. Have FirebaseApp.configure() inside AppDelegate.swift. An example is:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        FirebaseApp.configure()
        // Create the SwiftUI view that provides the window contents.
        let contentView = ContentView()

        // Use a UIHostingController as window root view controller.
        let window = UIWindow(frame: UIScreen.main.bounds)
        window.rootViewController = UIHostingController(rootView: contentView)
        self.window = window
        window.makeKeyAndVisible()
        return true
    }

The reason that I shared this gist is because I had some troubles setting the whole thing up but the docs are not that helpful to me so I had to do lots of research. But eventually it worked out and the docs are helpful in the end ;) I would like others to benefit from my discovery since I think this kind of research for some features that should be painless to implement are causing many people bunch of time. And hey, now you have a sample! Feel free to just refer from my code :)

Common Issues that I bumped into

1. How to test? Forget about the simulator, test with a real device! Apple ID on simulator is tricky
2. I got yellow 1000 errors: check capibility setting in your certificate and project settings, make sure that sign in with Apple is enabled
3. Firebase errors: Make sure you follow the setup guide in Firebase documentation carefuly!