var request = (HttpWebRequest)WebRequest.Create("www.xyz.com");
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.KeepAlive = false;
request.Headers.Add("Authorization", "Handshake");
byte[] bodyData;
bodyData = Encoding.UTF8.GetBytes(input_data);
request.ContentLength = bodyData.Length;
request.GetRequestStream().Write(bodyData, 0, bodyData.Length);
request.GetRequestStream().Flush();
request.GetRequestStream().Close();

using (var response = request.GetResponse())
{
    using (var reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8))
    {
       string output_data = reader.ReadToEnd();
    }

    response.Close();
}