A demonstration of a simple Android Fitbit client using Signpost authentication. Just add a consumer key and secret, and you're ready to run it.
Please note: I have only tested this on a 2013 Nexus 7. This is not a full Fitbit client, and it might not even be the start of a Fitbit client - at least not a good one anyways. But it should at least give you an idea of where to start.