How,and why, to implement Oauth in a rails application?

How,and why, to implement Oauth in a rails application?

So i'm creating an app that really only communicates with one other rails
application besides for some remote touch screens. The app is only
available to individuals who own one of these touch screens, and an admin.
Therefore, I really don't see the point in being able to sign in with
twitter, facebook, etc. However, I need SOME sort of http authentication
using request/access tokens in order to 1. authenticate a user and 2. be
able to derive what user is communicating with the server (and when). I've
spent about a week (I'm a rails newb) researching Oauth, omniauth, etc,
and I'm asking two things:
Because Im authenticating between my own two sets of apps, what gem would
be best for my situation?
Where would I write the logic for request/access tokens?
I really can't find any good tutorials for this