SoapEnvelope Security

Question

Hi, I have an XmlDoc which I would like to wrap in a SoapEnvelope then send it to a web service. I'm using a policy to enforce security on a soap message. the policy enforces that the message is signed with an X509 certificate, however, I'd like to add a usernameToken as well. If use webProxy.RequestSoapContext the UserNameToken is added to the message, however, if I create my own soapEnvelope and try to add the UsernameToken to it, the usernameToken is not added to the message or maybe the envelope is not actually sent to the webservice. How to send a custom created SoapEnvelope- including (singed certificate and usernameToken) considering the policy exists? thanks in advance, J