C# Post 模拟表单提交

        /// <summary>
        /// 向指定的URL地址发起一个POST请求。
        /// </summary>
        /// <param name="url">要请求的URL地址</param>
        /// <param name="keyvalues">要上传的数据项</param>
        /// <returns>服务器的返回结果</returns>
        public static string FormdataPost(string url, Dictionary<string, string> keyvalues, string Authorization)
        {
            System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;
 
            if (string.IsNullOrEmpty(url))
                throw new ArgumentNullException("url");
 
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.KeepAlive = true;
            request.Headers.Add("Authorization", Authorization);//token
 
            string boundary = "---------------------------" + Guid.NewGuid().ToString("N");
 
            byte[] boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");
 
 
            request.ContentType = "multipart/form-data; boundary=" + boundary;
 
 
            Stream stream = request.GetRequestStream();
 
            byte[] beginBoundaryBytes = Encoding.UTF8.GetBytes("--" + boundary + "\r\n");
            byte[] endBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");
 
            //写入参数
            if (keyvalues != null)
            {
                string formDataTemplate = "Content-Disposition: form-data; name=\"{0}\"\r\n\r\n" +
                       "{1}\r\n";
 
                foreach (string key in keyvalues.Keys)
                {
                    string formItem = string.Format(formDataTemplate, key, keyvalues[key]);
                    byte[] formItemBytes = Encoding.UTF8.GetBytes(formItem);
 
                    stream.Write(beginBoundaryBytes, 0, beginBoundaryBytes.Length); // 1.1 写入FormData项的开始边界符
                    stream.Write(formItemBytes, 0, formItemBytes.Length);   // 1.2 将键值对写入FormData项中
                }
            }
 
            boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
            stream.Write(boundaryBytes, 0, boundaryBytes.Length);
 
            stream.Close();
 
            using (WebResponse response = request.GetResponse())
            {
                using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8))
                {
                    return reader.ReadToEnd();
                }
            }
        }