public class HttpHelper
    {
        /// <summary>
        /// 访问失败的统一返回字符
        /// </summary>
        public String ErrorReturn { get; private set; } = "HttpHelper access error!";

        /// <summary>
        /// 登录后保存的cookie
        /// </summary>
        private CookieContainer Cookie = new CookieContainer();
        public string HttpWebRequestPost(string url, string param)
        {
            CookieContainer cookie = new CookieContainer();


            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);
            Encoding encoding = Encoding.UTF8;
            byte[] byteArray = Encoding.ASCII.GetBytes(param);
            string responseData = String.Empty;
            req.Method = "POST";
            req.ContentType = "application/x-www-form-urlencoded";
            //req.ContentLength = byteArray.Length;

            using (var streamWriter = new StreamWriter(req.GetRequestStream()))
            {
                streamWriter.Write(param);
                streamWriter.Flush();
                streamWriter.Close();
            }

            using (HttpWebResponse response = (HttpWebResponse)req.GetResponse())
            {
                using (StreamReader reader = new StreamReader(response.GetResponseStream(), encoding))
                {
                    responseData = reader.ReadToEnd();
                }
                return responseData;
            }
        }
        public string HttpGet(string Url, string postDataStr)
        {
            try
            {
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url + (postDataStr == "" ? "" : "?") + postDataStr);
                request.Method = "GET";
                request.ContentType = "text/html;charset=UTF-8";
                request.CookieContainer = Cookie;

                HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);//验证服务器证书回调自动验证

                Stream myResponseStream = response.GetResponseStream();
                StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
                string retString = myStreamReader.ReadToEnd();
                myStreamReader.Close();
                myResponseStream.Close();

                return retString;
            }
            catch (Exception ex)
            {

            }

            return ErrorReturn;
        }
        public bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {   // 总是接受  
            return true;
        }
    }