如何在Swift 3中访问输入到WKWebView中的用户名和密码

import WebKit

class ViewController: UIViewController, WKNavigationDelegate {
    var webView: WKWebView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let configuration = WKWebViewConfiguration()
        webView = WKWebView(frame: view.bounds, configuration: configuration)
        webView.navigationDelegate = self
        view.addSubview(webView)
    }
}

extension ViewController {
    func webView(_ webView: WKWebView, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
        if challenge.previousFailureCount == 0 {
            let credential = URLCredential(user: "username", password: "password", persistence: .forSession)
            completionHandler(.useCredential, credential)
        } else {
            completionHandler(.cancelAuthenticationChallenge, nil)
        }
    }
}