I've created a blog entry for some recent development I did to get Spring Social working with Spring Security via a AuthenticationFilter (as opposed to a SignInController).
Hopefully this will serve a couple of purposes:
1) It may be of use to other developers integrating Spring Social.
2) It should demonstrate a particular use-case for Spring Social authentication that the current SignInControllers do not address. As such, hopefully the developers for Spring Social will have a look, in particular at the hacks I had to do for it to work and consider if this in something they might want to look at in future releases.