How do I get HttpServletRequest, HttpServletResponse, etc. from within my advice without changing bar's signature?
I think that by using an ITD, you can introduce fields of those types annotated with @Context in Foo, which would then get injected by JAX-RS (as long as everything in your "etc." is part of the context). It's been a while since I last used ITDs, so I'm not sure if the fields are actually added to Foo directly; if they aren't, it won't work, of course.