No meu aplicativo iOS, eu gostaria de usar um WKWebView para agrupar um URL externo no aplicativo. Esse URL requer autenticação básica (ele precisa de credenciais de usuário e senha, como na captura de tela a seguir).

Depois de alguma investigação, estou tentando usardidReceiveAuthenticationChallenge para habilitar um login automático, então não estou entendendo como funciona.

Este é o meu código.

import UIKit
import WebKit

class WebViewController: UIViewController, WKNavigationDelegate {

    var webView: WKWebView?

    private var request : NSURLRequest {
        let baseUrl = "https://unimol.esse3.cineca.it/auth/Logon.do"
        let URL = NSURL(string: baseUrl)!
        return NSURLRequest(URL: URL)
    }

    /* Start the network activity indicator when the web view is loading */
    func webView(webView: WKWebView,
                 didStartProvisionalNavigation navigation: WKNavigation){
        UIApplication.sharedApplication().networkActivityIndicatorVisible = true
    }

    /* Stop the network activity indicator when the loading finishes */
    func webView(webView: WKWebView,
                 didFinishNavigation navigation: WKNavigation){
        UIApplication.sharedApplication().networkActivityIndicatorVisible = false
    }

    func webView(webView: WKWebView,
                 decidePolicyForNavigationResponse navigationResponse: WKNavigationResponse,
                                                   decisionHandler: ((WKNavigationResponsePolicy) -> Void)){
        decisionHandler(.Allow)
    }

    func webView(webView: WKWebView, didReceiveAuthenticationChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential?) -> Void) {

        if challenge.protectionSpace.host == "https://unimol.esse3.cineca.it/auth/Logon.do" {
            let user = "*******"
            let password = "******"
            let credential = NSURLCredential(user: user, password: password, persistence: NSURLCredentialPersistence.ForSession)
            challenge.sender?.useCredential(credential, forAuthenticationChallenge: challenge)
        }
    }

    override func viewDidLoad() {
        /* Create our preferences on how the web page should be loaded */
        let preferences = WKPreferences()
        preferences.javaScriptEnabled = false

        /* Create a configuration for our preferences */
        let configuration = WKWebViewConfiguration()
        configuration.preferences = preferences

        /* Now instantiate the web view */
        webView = WKWebView(frame: view.bounds, configuration: configuration)

        if let theWebView = webView {
            /* Load a web page into our web view */
            let urlRequest = self.request
            theWebView.loadRequest(urlRequest)
            theWebView.navigationDelegate = self
            view.addSubview(theWebView)
        }
    }
}

Estou diante dessa exceção:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Completion handler passed to -[MyUnimol.WebViewController webView:didReceiveAuthenticationChallenge:completionHandler:] was not called'

Se eu excluir odidReceiveAuthenticationChallenge método, eu sou capaz de acessar o URL, mas ele me fornece, inconscientemente, credenciais incorretas.

Alguém poderia me explicar o que estou fazendo de errado, por favor?