I can't seem to find one that's been updated recently. If none, is there a good Java library for doing the necessary signature verification, base64 decoding, etc operations needed to interact with Facebook's API?
UPDATE: I'm using Spring Social Facebook to aid in working with Facebook. It doesn't handle everything and isn't perfect, but the best library out there for Java. Looking forward to the ongoing progress from Spring. I asked a couple questions in their forum and responses were informative and super quick.
You can check facebook's official android SDK which is written in Java:
https://github.com/facebook/facebook-android-sdk
all basic things like verification, decoding, etc are there, maybe android-related stuff is not what you need but I guess it is relatively trivial to extract it from there.
hope this helps