AppleSignIn Singleton to use in SwiftUI

AppleSignIn.swift

//
//  AppleSignIn.swift
//

import Foundation
import FirebaseAuth
import AuthenticationServices
import CryptoKit

final class AppleSignIn: NSObject {
    
    static let sharedInstance = AppleSignIn()
    
    fileprivate var currentNonce: String?
    
    func appleSignIn() {
        let nonce = randomNonceString()
        currentNonce = nonce
        let appleIDProvider = ASAuthorizationAppleIDProvider()
        let request = appleIDProvider.createRequest()
        request.requestedScopes = [.email]
        request.nonce = sha256(nonce)
        
        let authorizationController = ASAuthorizationController(authorizationRequests: [request])
        authorizationController.presentationContextProvider = UIApplication.shared.windows.last?.rootViewController as? ASAuthorizationControllerPresentationContextProviding
        authorizationController.delegate = self
        authorizationController.performRequests()
    }
    
    // MARK: Some utilities
    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
    }
    
    private func randomNonceString(length: Int = 32) -> String {
      precondition(length > 0)
      let charset: Array<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
    }
}


extension AppleSignIn: ASAuthorizationControllerDelegate {
    func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
        print("WE ARE HERE!")
        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 let error = 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.
            // ...
            print("User is now connectedr")
          }
        }
    }
    
    func authorizationController(controller: ASAuthorizationController, didCompleteWithError error: Error) {
        print("Error Signing in with Apple ID: \(error.localizedDescription)")
    }
}