用C#调用接口做登录和发短信的功能如何做？？

private static readonly string DefaultUserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";
        /// 
  
        /// 创建POST方式的HTTP请求  
        /// 
  
        /// 请求的URL  
        /// 随同请求POST的参数名称及参数值字典  
        /// 请求的超时时间  
        /// 请求的客户端浏览器信息，可以为空  
        /// 发送HTTP请求时所用的编码  
        /// 随同HTTP请求发送的Cookie信息，如果不需要身份验证可以为空  
        ///   
        public static string PostHttpResponse(string url, Dictionary parameters,
            int? timeout)
        {
            try
            {
                if (string.IsNullOrEmpty(url))
                {
                    throw new ArgumentNullException("url");
                }
                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
                request.ServicePoint.Expect100Continue = false;
                request.ServicePoint.UseNagleAlgorithm = false; //是否使用 Nagle 不使用 提高效率
                //request.AllowWriteStreamBuffering = false; //数据是否缓冲 false 提高效率
                request.Method = "POST";
                request.ContentType = "application/x-www-form-urlencoded";
                request.UserAgent = DefaultUserAgent;
                if (timeout.HasValue)
                {
                    request.Timeout = timeout.Value;
                }
                else
                {
                    request.Timeout = 20000;
                }
                Encoding requestEncoding = Encoding.GetEncoding("UTF-8");
                //如果需要POST数据  
                if (!(parameters == null || parameters.Count == 0))
                {
                    StringBuilder buffer = new StringBuilder();
                    int i = 0;
                    foreach (string key in parameters.Keys)
                    {
                        if (i > 0)
                        {
                            buffer.AppendFormat("&{0}={1}", key, parameters[key]);
                        }
                        else
                        {
                            buffer.AppendFormat("{0}={1}", key, parameters[key]);
                        }
                        i++;
                    }
                    byte[] data = requestEncoding.GetBytes(buffer.ToString());
                    using (Stream stream = request.GetRequestStream())
                    {
                        stream.Write(data, 0, data.Length);
                    }
                }

                //获取响应，并设置响应编码
                HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                string encoding = response.ContentEncoding;
                if (encoding == null || encoding.Length < 1)
                {
                    encoding = "UTF-8"; //默认编码
                }
                //读取响应流
                StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(encoding));
                string returnData = reader.ReadToEnd();
                reader.Dispose();
                response.Close();
                return returnData;
            }
            catch (Exception ex)
            {
                MessageUtil.ShowWarning(ex.Message);
            }
            return "";
        }

请求接口的方法

Dictionary parameters = new Dictionary();
            parameters.Add("USER_ACCOUNT", UserName);
            parameters.Add("USER_PASSWORD", pwd);
            return HttpPostHelper.PostHttpResponse("接口URL", parameters, null);