In Hadoop, you can create a plugin using a Hadoop API that talks to your datastore for handling user to group mapping. It doesn't seem that the Access Control Lists are exposed via API, but maybe I just missed it.
Anyone know if this is actually possible..
For groups, you create a class that overrides the public List<String> getGroups(String user) throws IOException; method
and tweak the Hadoop config to use your group mapper.