/// <summary>
        /// 获取access_token
        /// </summary>
        /// <returns></returns>
        public string GetToken()
        {
            string url = "https://XXX.com/oauth/token?client_id=XX";

            byte[] data = System.Text.Encoding.UTF8.GetBytes("");//参数

            HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(url);

            myRequest.Headers["Authorization"] = "XX"; //添加头
            myRequest.Method = "POST";//请求类型 Get,Post....
            myRequest.ContentType = "application/xml;charset=UTF-8";//内容格式



            myRequest.ContentLength = data.Length;

            Stream newStream = myRequest.GetRequestStream();
            newStream.Write(data, 0, data.Length);
            newStream.Close();


            HttpWebResponse myResponse = myRequest.GetResponse() as HttpWebResponse;
            StreamReader reader = new StreamReader(myResponse.GetResponseStream(), Encoding.UTF8);
            string content = reader.ReadToEnd();
            reader.Close();
            return content;
        }