Changes needed for foreman-katello-engine to work

The Foreman engine to expose some Katello features [1] request the following
changes:

* make oauth to work: there was a problem with ActionDispatch::Request not
  being supported by oauth gem, fixing by using Rack::Request instead

* include pool details from Candlepin when exposing activation keys through
  REST API

[1] - https://github.com/Katello/foreman-katello-engine