/// <summary>

        /// 获取Access token

        /// </summary>

        /// <param name="appid"></param>

        /// <param name="secret"></param>

        /// <returns></returns>

        public static string GetAccessToken()

        {

            //创建一个配置

            var Configuration = new ConfigurationBuilder()

                  //添加配置文件

                  .Add(new JsonConfigurationSource { Path = "appsettings.json", ReloadOnChange = true })

                  .Build();

            //赋值

            _config = Configuration;

            //读取key和secret

            string appid = _config["WeiXingSession:AppID"];

            string secret = _config["WeiXingSession:AppSecret"];

            string strJson = HttpRequestUtil.RequestUrl(string.Format("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid={0}&secret={1}", appid, secret));

            return GetJsonValue(strJson, "access_token");

        }

  /// <summary>

        /// HTTP请求功能

        /// </summary>

        internal class HttpRequestUtil

        {

            #region 请求Url，不发送数据

            /// <summary>

            /// 请求Url，不发送数据

            /// </summary>

            public static string RequestUrl(string url)

            {

                return RequestUrl(url, "POST");

            }

            #endregion

            #region 请求Url，不发送数据

            /// <summary>

            /// 请求Url，不发送数据

            /// </summary>

            public static string RequestUrl(string url, string method)

            {

                // 设置参数

                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;

                CookieContainer cookieContainer = new CookieContainer();

                request.CookieContainer = cookieContainer;

                request.AllowAutoRedirect = true;

                request.Method = method;

                request.ContentType = "text/html";

                request.Headers.Add("charset", "utf-8");

                //发送请求并获取相应回应数据

                HttpWebResponse response = request.GetResponse() as HttpWebResponse;

                //直到request.GetResponse()程序才开始向目标网页发送Post请求

                Stream responseStream = response.GetResponseStream();

                StreamReader sr = new StreamReader(responseStream, Encoding.UTF8);

                //返回结果网页（html）代码

                string content = sr.ReadToEnd();

                return content;

            }

            #endregion

        }

public static string GetJsonValue(string jsonStr, string key)

        {

            string result = string.Empty;

            if (!string.IsNullOrEmpty(jsonStr))

            {

                key = "\"" + key.Trim('"') + "\"";

                int index = jsonStr.IndexOf(key) + key.Length + 1;

                if (index > key.Length + 1)

                {

                    //先截逗号，若是最后一个，截“｝”号，取最小值

                    int end = jsonStr.IndexOf(',', index);

                    if (end == -1)

                    {

                        end = jsonStr.IndexOf('}', index);

                    }

                    result = jsonStr.Substring(index, end - index);

                    result = result.Trim(new char[] { '"', ' ', '\'' }); //过滤引号或空格

                }

            }

            return result;

        }