HTTP Proxy authentication for JBossWS Web Service clients

We need a possibility to access Web Service endpoints through an HTTP Proxy which needs client authentication. In our case it's BASIC authentication, but there are may other JBoss customers who want to have support for other authentication schemas like DIGEST or NTLM.

There must be a way to set the Proxy settings, especially the Proxy credentials used for authentication (username, password), in some sort of meta data (using a Java API).