HttpWebRequest handler = (HttpWebRequest)WebRequest.Create("someUrl");
handler.Method = "POST";

string postData = "some data";

byte[] data = Encoding.ASCII.GetBytes(postData);
handler.ContentLength = data.Length;
using (var stream = handler.GetRequestStream())
{
    stream.Write(data, 0, data.Length);
}
handler.ContentType = "application/xml; charset=utf-8";
HttpWebResponse response = (HttpWebResponse)handler.GetResponse();

<security mode="Transport"/>