HttpClient.cs

var http = new HttpClient();
// GET request
var getRequest = "http://hroch486.icpf.cas.cz/cgi-bin/echo.pl?key=value";
var getResponse = await http.GetAsync(getRequest);
var getResult = await getResponse.Content.ReadAsStringAsync();
// POST request
var postUri = new Uri("http://hroch486.icpf.cas.cz/cgi-bin/echo.pl");
var postFields = new Dictionary<string, string>
  {
    { "key", "value" }
  };
var postContent = new FormUrlEncodedContent(postFields);
var postResponse = await http.PostAsync(postUri, postContent);
var postResult = await postResponse.Content.ReadAsStringAsync();