Estou tentando buscar eventos do calendário no meu aplicativo iOS. Então, para isso, criei um projeto no console do desenvolvedor do Google e obtive o Client ID, ApiKey.

E pods instalados com

pod 'GoogleAPIClient/Calendar', '~> 1.0.2'
pod 'GTMOAuth2', '~> 1.1.0'
pod 'Google/SignIn'

E depois de assinar no Gmail, é pedir permissão para acessar o Calendário, até que funcione bem, mas, ao buscar os eventos que mostram o seguinte erro.

error   NSError domain: "com.google.GTLJSONRPCErrorDomain" - code: 401  0x0000604000646330

E meu código é segue

private let scopes = [kGTLAuthScopeCalendar]

private let service = GTLServiceCalendar()

private let kApiKey = "someKey"

let output = UITextView()

private let kKeychainItemName = "Google Calendar API"

private let kClientID = "SomeID"

func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {

    if (error == nil) {


    } else {
        print("\(error.localizedDescription)")
    }

    if user != nil {
        output.frame = view.bounds
        output.isEditable = false
        output.contentInset = UIEdgeInsets(top: 20, left: 0, bottom: 20, right: 0)
        output.autoresizingMask = [.flexibleHeight, .flexibleWidth]

        view.addSubview(output);

        if let auth = GTMOAuth2ViewControllerTouch.authForGoogleFromKeychain(
            forName: kKeychainItemName,
            clientID: kClientID,
            clientSecret: nil) {
            service.authorizer = auth
        }

        print("\(user)")
        service.authorizer = user.authentication.fetcherAuthorizer()
        fetchEvents()
    }

}

func fetchEvents() {

    let query = GTLQueryCalendar.queryForEventsList(withCalendarId: "primary")

    query?.maxResults = 10
    query?.singleEvents = true
    query?.orderBy = kGTLCalendarOrderByStartTime
    service.executeQuery(
        (query)!,
        delegate: self,
        didFinish: #selector(displayResultWithTicket(ticket:finishedWithObject:error:)))
}

// Display the start dates and event summaries in the UITextView

@objc func displayResultWithTicket(

    ticket: GTLServiceTicket,
    finishedWithObject response : GTLCalendarEvents,
    error : NSError?) {

    if let error = error {
        showAlert(title: "Error", message: error.localizedDescription)
        return
    }

    var eventString = ""

    if let events = response.items(), !events.isEmpty {
        for event in events as! [GTLCalendarEvent] {
            print(event)
        }
    } else {
    print("No upcoming events found.")
  }
}

   func showAlert(title: String, message: String) {

    let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "Thank You", style: UIAlertActionStyle.default, handler: nil))
    self.present(alert, animated: true, completion: nil)

    }    

override func viewDidLoad() {
    super.viewDidLoad()

    GIDSignIn.sharedInstance().clientID = kClientID
    GIDSignIn.sharedInstance().uiDelegate = self
    GIDSignIn.sharedInstance().scopes = scopes
    GIDSignIn.sharedInstance().signIn()
    GIDSignIn.sharedInstance().delegate = self
    service.apiKey = kApiKey
}

Mesmo que eu verifiquei alguns fóruns, não obtive nenhuma solução para isso.

Alguém pode me sugerir onde estou errado?