SoapWithoutWcf.cs

protected static WebRequest CreateRequest(string url, string secret)
{
  var xml = @"
<soapenv:Envelope xmlns:soapenv=""http://schemas.xmlsoap.org/soap/envelope/"" xmlns:ns=""https://service/1/0"">
    <soapenv:Header/>
    <soapenv:Body>
        <ns:Request>
            <ns:FirstName>XXX</ns:FirstName>
            <ns:LastName>YYY</ns:LastName>
        </ns:Request>
    </soapenv:Body>
</soapenv:Envelope>";

  var c = Encoding.UTF8.GetBytes(xml);

  var wr = (HttpWebRequest)WebRequest.Create(url);
  wr.ProtocolVersion = HttpVersion.Version11;
  wr.ContentType = "text/xml;charset=utf-8";
  wr.ContentLength = xml.Length;
  wr.Accept = "text/xml";
  wr.Headers.Add("SOAPAction", "\"\"");
  wr.Headers.Add("Secret", secret);
  wr.Method = "POST";
  wr.GetRequestStream().Write(c, 0, c.Length);

  return wr;
}