So right now I have a POC that I think works pretty well.

Demo : https://plus.google.com/106588661437153585722/posts/XbAmMJ6Ltbg

Code : https://github.com/secondsun/aerogear-android-authz/tree/AGDROID-319

It is API compatible with what we have now, but it only works for OAuth2 services which allow custom redirect schemas.