向WebProxy传递凭据

对于我正在使用的服务，我有一个自定义HTTP类。最终，它将以方法的形式包含特定于服务的请求。我需要做的是设置用户提供的代理的凭据，例如，如果用户有一个代理列表。

下面是我的代码。我已经注释了需要设置凭据的部分。我看过MSDN上的icredential类，但我不知道如何从字符串设置它们。

class RequestClass
{
    private CookieContainer cookieJar;
    private WebProxy proxy = null;
    public RequestClass()
    {
        this.cookieJar = new CookieContainer();
    }
    public RequestClass(String proxyURL, int port)
    {
        this.proxy = new WebProxy(proxyURL, port);
    }
    public RequestClass(String proxyURL, int port, String username, String password)
    {
        this.proxy = new WebProxy(proxyURL, port);
        // Need to set them here
    }
    // HTTP Get Request
    public HttpWebResponse getRequest(String url, NameValueCollection headers)
    {
        HttpWebRequest getRequest = (HttpWebRequest)WebRequest.Create(url);
        getRequest.Method = "GET";
        getRequest.CookieContainer = cookieJar;
        foreach (String key in headers.Keys)
        {
            getRequest.Headers.Add(key, headers[key]);
        }
        return (HttpWebResponse)getRequest.GetResponse();
    }
    // HTTP Post Request
    public HttpWebResponse postRequest(String url, String postData, NameValueCollection headers)
    {
        byte[] postBytes = Encoding.ASCII.GetBytes(postData);
        HttpWebRequest postRequest = (HttpWebRequest)WebRequest.Create(url);
        postRequest.Method = "POST";
        postRequest.CookieContainer = cookieJar;
        postRequest.ContentLength = postBytes.Length;
        postRequest.ProtocolVersion = HttpVersion.Version10;
        foreach(String key in headers.Keys)
        {
            postRequest.Headers.Add(key, headers[key]);
        }
        Stream postRequestStream = postRequest.GetRequestStream();
        postRequestStream.Write(postBytes, 0, postBytes.Length);
        postRequestStream.Close();
        return (HttpWebResponse)postRequest.GetResponse();
    }
}

}

public RequestClass(String proxyURL, int port, String username, String password)
{
    //Validate proxy address
    var proxyURI = new Uri(string.Format("{0}:{1}", proxyURL, port));
    //Set credentials
    ICredentials credentials = new NetworkCredential(username, password);
    //Set proxy
    this.proxy =  = new WebProxy(proxyURI, true, null, credentials );
}

public System.Net.IWebProxy RequestClass(String proxyURL, int port, String username, String password)
    {
        //Validate proxy address
        var proxyURI = new Uri(string.Format("{0}:{1}", proxyURL, port));
        //Set credentials
        ICredentials credentials = new NetworkCredential(username, password);
        //Set proxy
       return new WebProxy(proxyURI, true, null, credentials);
    }

using System;
using System.Net;
public class RequestClass
{
    private WebProxy proxy = null;
    public RequestClass(string url, int port, string username, string password)
    {
        // Prepare URL
        var urlBuilder = new UriBuilder(url);
        urlBuilder.Port = port;
        // Setup credentials
        var credentials = new NetworkCredential(username, password);
        // Setup proxy
        this.proxy = new WebProxy(urlBuilder.Uri, true, null, credentials);
    }
}