Вот пример C# кода, да, вы используете объект HttpContext.Request
using (Stream stream = Request.InputStream)
{
int streamLen = Convert.ToInt32(Request.InputStream.Length);
byte[] streamArray = new byte[streamLen];
// Read stream into byte array.
int streamRead = stream.Read(streamArr, 0, streamLen);
requestContents = Encoding.UTF8.GetString(streamArrary);
var serializer = new XmlSerializer(typeof(EnvelopeInformation));
stream.Position = 0;
var xmlTextReader = new TextReader(stream);
envelopeInformation = (EnvelopeInformation)serializer.Deserialize(xmlTextReader);
}