how to send username and password in soap C#

WebRequest request = (HttpWebRequest)WebRequest.Create(endPoint);
        request.Method = "POST";

        byte[] byteArray = Encoding.UTF8.GetBytes(requestMesg);
        request.ContentLength = byteArray.Length;

        request.ContentType = "application/soap+xml;charset=UTF-8";

        NetworkCredential creds = new NetworkCredential("username", "password");
        request.Credentials = creds;

        Stream datastream = request.GetRequestStream();
        datastream.Write(byteArray, 0, byteArray.Length);
        datastream.Close();

        WebResponse response = request.GetResponse();
        datastream = response.GetResponseStream();

        StreamReader reader = new StreamReader(datastream);

        respMesg = reader.ReadToEnd().ToString();

        reader.Close();