с использованием
using System.Net.Http;
и ваш код будет
var url = "http://yoursite.com/Home/Insert";
var data = new {"recipient"= "stefan.", "body"="Test"};
using(var client = new HttpClient())
{
var response = await client.PostAsJsonAsync(url, data);
string responseContent = await response.Content.ReadAsStringAsync(); // only to see response as text ( debug perpose )
var result = await ProcessedResult<TResult>(response); // cast it to TResult or any type that you expect to retrieve
}