I know this post is a little old, but since google always directs me to this one when I search for an Android OAuth 2.0 library, I think I need to tell you about OAuth2Android:
Currently it supports Bearer-Tokens and MAC-Tokens based on the
specifications:
draft-ietf-oauth-v2-16
draft-ietf-oauth-v2-bearer-06
draft-ietf-oauth-v2-http-mac-00
Other extensions are also possible and it will be updated.
You need at least Android Platform Version 2.3.3; API Level 10.
You can get it here:
https://github.com/Xotan/OAuth2Android
or
git@github.com:Xotan/OAuth2Android.git
regards Christoph