There is a security example in subversion that shows how to do this. However, I think I'm going to go ahead and make the proposed changes to ClientFacade. So for security, you will get a WebConversation from the WebConversationFactory, then set the credentials and pass that into the constructor of the ClientFacade. From there you can continue with a user session.
It shouldn't take more than a day or two to finish the changes. I'll post when it is done and I'll update the example.