Use iCloud SafariKeychain from Swift5

SafariKeychain.swift

//
//  SafariKeychain.swift
//  Positipp
//
//  Created by Rafael Bartolome on 15/06/2019.
//  Copyright © 2019 Moonshot People Tech SL. All rights reserved.
//

import Foundation

extension String: Error {}

typealias SafariKeychainCheckCompletion = (Result<(String?, String?), Error>) -> Void
typealias SafariKeychainUpdateCompletion = (Result<Void, Error>) -> Void

class SafariKeychain {
	enum Constants {
		/// Error code for when there are no accounts associated with the domain
		static let SafariKeychainErrorCodeNoAccount = -25300
		/// Error code for when the entitlements aren't setup correctly.
		static let SafariKeychainErrorCodeNoDomain = -50
		#warning("TODO: Update domain to your domain")
		static let Domain = "example.com"
	}
}

extension SafariKeychain {
	/// Request the credentials information stored in safari keychain
	func checkSafariCredentials(completion: @escaping SafariKeychainCheckCompletion) {
		SecRequestSharedWebCredential(Constants.Domain as CFString?, .none) { (credentials, error) -> () in
			var username: String?
			var password: String?

			if let error = error {
				return completion(.failure(error))
			}
			if let credentials = credentials {
				let credentialsArray =  credentials as NSArray
				if credentialsArray.count > 0 {
					if let credentials = credentialsArray[0] as? [String: String] {
						if let account = credentials[String(kSecAttrAccount)] {
							username = account
						}
						if let sharedPassword = credentials[String(kSecSharedPassword)] {
							password = sharedPassword
						}
						DispatchQueue.main.async {
							completion(.success((username, password)))
						}
						return
					}
				}
			} else {
					//User cancelled the operation
					DispatchQueue.main.async {
						completion(.failure("User cancel operation"))
					}
					return
			}

			DispatchQueue.main.async {
				completion(.failure("General error"))
			}
		}
	}


	/// Update the credentials information in safari keychain or remove the current ones by passing a nil password.
	func updateSafariCredentials(userName: String,
								 password: String? = nil,
								 completion: @escaping SafariKeychainUpdateCompletion) {
		SecAddSharedWebCredential(Constants.Domain as CFString, userName as CFString, password as CFString?) { error -> () in
			if let error = error {
				completion(.failure(error))
			} else {
				completion(.success(()))
			}
		}
	}
}

Thank you so much Rafael

Glad I could help.