WebClient不会返回PHPSESSID

Question

我有一个CookieAwareWebClient

public class CookieAwareWebClient : WebClient
{
    private CookieContainer cookie = new CookieContainer();

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

        }
        return request;
    }

}

我正在使用这个类来登录网页，它的工作正常。我想获取cookie值并在GUI中显示它。我从浏览器获得的Cookie值是

  

PHPSESSID = 8m3vbs6bpt8utj7st64qe9nvd5;安全=低

然而，当我在程序中请求cookie时;

client.ResponseHeaders["Set-Cookie"];

返回“security = low”

我如何获得PHPSESSID？提前致谢