Sign In with Apple: handle login result

*.swift

extension MyLoginViewController: ASAuthorizationControllerDelegate {
    func authorizationController(controller: ASAuthorizationController,    
                                   didCompleteWithAuthorization authorization: ASAuthorization) {
        if let appleIDCredential = authorization.credential as? ASAuthorizationAppleIDCredential {

            let userIdentifier = appleIDCredential.user
            let fullName = appleIDCredential.fullName
            let email = appleIDCredential.email

            // Now we have the account information.
            // We can store the userIdentifier in our account 
            // system as the username.
        } else if let passwordCredential = authorization.credential as? ASPasswordCredential {
            // Sign in using an existing iCloud Keychain credential.
            let username = passwordCredential.user
            let password = passwordCredential.password
            
            // handle being logged in the old way
        }
     }
}