Rails API and Ember, Android and iOS. Is OAuth2 the best way to Login and protect API?

I'm getting crazy to understand what is the best for an app Rails based and authentication / authorization on it.

I'm using Rails-API (or the new Rails 5) as a backend for my APIs.

Then I have Ember for an HTML client in browser, an android App and an iOS app using the same APIs from my Rails.

Is Oauth2 the best?

I'm reading about Resource Owner Password Credentials flow, which is used by EmberSimpleAuth, but i'm stucked.

I'm using Doorkeeper gem with Rails, at github master version. But I can't login with my EmberSimpleAuth.

Is this a good way of doing it? There is another way of protect my APIs?