//地址
string _url = "https://www.dXXXayup.ink/api/User/Login";
//json参数
string jsonParam = "{ phonenumber:"18665885202",pwd:"tsp"}";
var request = (HttpWebRequest)WebRequest.Create(_url);
request.Method = "POST";
request.ContentType = "application/json;charset=UTF-8";
byte[] byteData = Encoding.UTF8.GetBytes(jsonParam);
int length = byteData.Length;
request.ContentLength = length;
Stream writer = request.GetRequestStream();
writer.Write(byteData, 0, length);
writer.Close();
var response = (HttpWebResponse)request.GetResponse();
var responseString = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("utf-8")).ReadToEnd();
MessageBox.Show(responseString.ToString());