Or in restSharp:
var client = new RestClient("https://example.com/?urlparam=true");
var request = new RestRequest(Method.POST);
request.AddHeader("content-type", "application/x-www-form-urlencoded");
request.AddHeader("cache-control", "no-cache");
request.AddHeader("header1", "headerval");
request.AddParameter("application/x-www-form-urlencoded", "bodykey=bodyval", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);