Rails devise, find current_user by session_store key

We have a production system (main app) running on Rails with devise gem configured (using Redis session store)(session is enabled for all subdomain)

I need to build a custom authentication service for one our subdomain based microservice. For each request, this microservice will be calling our main app with the cookie value of rails session store key (which is configured in config/initializers/session_store.rb).

So the question is, can I find the user mapped to that cookie value (or session)? (Using Devise or Warden)