使用WebClient通过登录访问受保护的页面

Question

我正在尝试访问受“登录表单”保护的页面。 我已经检查了SO中的主题，并且找到了使用Cookie的WebClient扩展：

public class CookieAwareWebClient : WebClient
{
    public CookieAwareWebClient()
    {
        this.CookieContainer = new CookieContainer();
    }

    public CookieContainer CookieContainer { get; private set; }

    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest request = base.GetWebRequest(address);
        if (request is HttpWebRequest)
        {
            (request as HttpWebRequest).CookieContainer = this.CookieContainer;
        }
        return request;
    }
}

在互联网的更多帮助下，我想到了以下代码：

using (var webClient = new CookieAwareWebClient())
        {
            try
            {
                NameValueCollection collection = new NameValueCollection
                {
                    {"UserName", userName},
                    {"Password", password}
                };

                webClient.UploadValues("https://judge.softuni.bg/Account/Login", "POST", collection);


                string result = webClient.DownloadString("https://judge.softuni.bg/Contests/Compete/Results/Simple/104");

            }
            catch (WebException webException)
            {
                MessageBox.Show(webException.Status.ToString());
            }
        }

最后，在“结果”字符串中，我具有带有Form操作的登录页面，如果我登录该页面，它将重定向到所需页面。有什么想法我做错了吗？