A: HttpClient  using System.Net.Http;

B:RestSharp   using Flurl.Http;

C:HttpWebRequest (Not recommended for new work)    

using System.Net;using System.Text; // for class Encodingusing System.IO; // for StreamReader

https://stackoverflow.com/questions/4015324/how-to-make-http-post-web-request/4015346?r=SearchResults#4015346