Try to use this:
using (var handler = new HttpClientHandler() { CookieContainer = new CookieContainer() })
{
using (var client = new HttpClient(handler) { BaseAddress = new Uri("site.com") })
{
//add parameters on request
var body = new List<KeyValuePair<string, string>>
{
new KeyValuePair<string, string>("test", "test"),
new KeyValuePair<string, string>("test1", "test1")
};
HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, "site.com");
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/x-www-form-urlencoded; charset=UTF-8"));
client.DefaultRequestHeaders.Add("Upgrade-Insecure-Requests", "1");
client.DefaultRequestHeaders.Add("X-Requested-With", "XMLHttpRequest");
client.DefaultRequestHeaders.Add("X-MicrosoftAjax", "Delta=true");
//client.DefaultRequestHeaders.Add("Accept", "*/*");
client.Timeout = TimeSpan.FromMilliseconds(10000);
var res = await client.PostAsync("", new FormUrlEncodedContent(body));
if (res.IsSuccessStatusCode)
{
var exec = await res.Content.ReadAsStringAsync();
Console.WriteLine(exec);
}
}
}