如何使用C#程序登录网站

我想使用C#登录此网站：这是我的尝试，但它把我送到了第一页。没有给我返回下一个页面，登录后应该可以看到，请帮助我解决这个问题：

string formParams = 
string.Format("mail={0}&password={1}", store@admin.com", "admin");
      string cookieHeader;
      WebRequest req = WebRequest.Create("http://muslimgowns.com/dashboard/login/public_login");
            req.ContentType = "application/x-www-form-urlencoded";
            req.Method = "POST";
            byte[] bytes = Encoding.ASCII.GetBytes(formParams);
            req.ContentLength = bytes.Length;
            using (Stream os = req.GetRequestStream())
            {
                os.Write(bytes, 0, bytes.Length);
            }
            WebResponse resp = req.GetResponse();
            cookieHeader = resp.Headers["Set-cookie"];
            using (StreamReader sr = new  StreamReader(resp.GetResponseStream()))
            {
                string pageSource = sr.ReadToEnd();
                File.AppendAllText("first.txt", pageSource);
            }
            string pageSource1;
            string getUrl = "http://muslimgowns.com/dashboard/home";
            WebRequest getRequest = WebRequest.Create(getUrl);
            getRequest.Headers.Add("Cookie", cookieHeader);
            WebResponse getResponse = getRequest.GetResponse();
            using (StreamReader sr = new StreamReader(getResponse.GetResponseStream()))
            {
                pageSource1 = sr.ReadToEnd();
                File.AppendAllText("second.txt", pageSource1);
            }
        }