How to send x.509 Cert with request

We have a Http Remoting Service protected using Spring Security. The authentication method we are using is an x.509 certificate. The configuration of the server was fairly easy, what I am struggling with right now is how to get the client to send an x.509 certificate.

The client is a stand-alone java application. I am overriding the httpInvokerRequestExecutor. The hope there was to modify the post, but the method of attaching the certificate still eludes me.

Any help with this would be greatly appreciated.

Thanks!