basic implementation of auth

Just added a basic implementation of auth here so I could test my own projects being able to handle login issues if a token is removed.
Looking good! I think auth here should always return an object. It looks like, in fact, that it returns whatever was originally in the variables passed into the token during creation. I don't think we want to get that sophisticated, but perhaps it should at least be an object for consistency with the Firebase specs; something like:

    { auth: { id: 'test', _token: token }, expires: ... }

Other than this, everything looks ready to merge. The travis failures were a timeout, so those may be irrelevant.