SwiftUI - Firebase, Sign In With Apple, custom Button

Question

I would like to create my own SignInWithAppleButton with my own design, following the guidelines of course.

I am having trouble translating the startSignInWithAppleFlow function from Swift to SwiftUI.

struct ContentView: View {
    
    var body: some View {
        ...
        AuthButton(title: "Connect with Apple", iconName: "appleIcon") {
            authViewModel.signInWithApple()
        }
        ...
    }
}

struct AuthButton: View {
    let title: String
    let iconName: String
    let action: () -> Void

    var body: some View {
        Button {
            action()
        } label: {
            RoundedRectangle(cornerRadius: 16)
                .fill(.clear)
                .frame(height: 80)
                .overlay(
                    Text(title)
                        .font(.regular16)
                        .foregroundColor(.black)
                )
                .overlay(
                    HStack {
                        HorizontalSpacer(width: 32)
                        Image(iconName)
                            .resizable()
                            .frame(width: 30, height: 30, alignment: .center)
                        Spacer()
                    }
                )
        }
        .buttonStyle(AuthButtonStyle())
    }
}

class AuthenticationViewModel: ObservableObject {
    func signInWithApple() {
        Unclear what should be here!
    }

    private func randomNonceString(length: Int = 32) -> String {
        precondition(length > 0)
        let charset: [Character] =
            Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")
        var result = ""
        var remainingLength = length

        while remainingLength > 0 {
            let randoms: [UInt8] = (0 ..< 16).map { _ in
                var random: UInt8 = 0
                let errorCode = SecRandomCopyBytes(kSecRandomDefault, 1, &random)
                if errorCode != errSecSuccess {
                    fatalError(
                        "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)"
                    )
                }
                return random
            }

            randoms.forEach { random in
                if remainingLength == 0 {
                    return
                }

                if random < charset.count {
                result.append(charset[Int(random)])
                remainingLength -= 1
                }
            }
        }

        return result
    }

    private 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
    }
}

Answer 1

It looks like you're on step 2 of the documentation.

Your function would look like this:

func signInWithApple() {
  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.performRequests()
}

Answer 2

This is what I currently use - modify the code for your own use. I just bind the isUserAuthenticated to know when sign In is complete and call performSignIn on the custom button.

import SwiftUI
import AuthenticationServices
import CryptoKit
import Combine
import FirebaseAuth

class SignInWithAppleManager: NSObject, ObservableObject, ASAuthorizationControllerDelegate, ASAuthorizationControllerPresentationContextProviding {

    @Published var isUserAuthenticated = false
    var currentNonce: String?

    func performSignIn() {
        let request = createAppleIdRequest()
        let authorizationController = ASAuthorizationController(authorizationRequests: [request])

        authorizationController.delegate = self
        authorizationController.presentationContextProvider = self

        authorizationController.performRequests()
    }

    private func createAppleIdRequest() -> ASAuthorizationRequest  {
        let appleIDProvider = ASAuthorizationAppleIDProvider()
        let request = appleIDProvider.createRequest()
        request.requestedScopes = [.email]

        let nonce = randomNonceString()
        request.nonce = sha256(nonce)
        currentNonce = nonce

        return request
    }

    private 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
    }

    private func randomNonceString(length: Int = 32) -> String {
       precondition(length > 0)
       let charset: [Character] =
       Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")
       var result = ""
       var remainingLength = length
       
       while remainingLength > 0 {
           let randoms: [UInt8] = (0 ..< 16).map { _ in
               var random: UInt8 = 0
               let errorCode = SecRandomCopyBytes(kSecRandomDefault, 1, &random)
               if errorCode != errSecSuccess {
                   fatalError(
                       "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)"
                   )
               }
               return random
           }

           randoms.forEach { random in
               if remainingLength == 0 {
                   return
               }
               
               if random < charset.count {
                   result.append(charset[Int(random)])
                   remainingLength -= 1
               }
           }
       }
       return result
   }

    func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
        if let appleIDCredential = authorization.credential as? ASAuthorizationAppleIDCredential {
            guard let nonce = currentNonce else  {
                fatalError("DEBUG: Invalid state: A login callback was recieved, but no login request was sent")
            }
            guard let appleIDToken = appleIDCredential.identityToken else {
                print("DEBUG: Unable to fetch identity token")
                return
            }
            guard let idTokenString = String(data: appleIDToken, encoding: .utf8) else {
                print("DEBUG: Unable to serialize token string from data \(appleIDToken.debugDescription)")
                return
            }
            
            let credential = OAuthProvider.credential(withProviderID: "apple.com", idToken: idTokenString, rawNonce: nonce)
            Auth.auth().signIn(with: credential) { result, error in
                self.isUserAuthenticated = true
            }
        }
    }

    func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
        return (UIApplication.shared.connectedScenes.first as? UIWindowScene)?.windows.first ?? UIWindow()
    }
}