ruby on rails - Shared authentication with devise -

i have 2 rails 4 sites, auth.example.com , app.example.com. there going multiple app-type sites, maybe dozen or two, let's start one. auth has devise set can basic user management (user creation , deactivation, password , ssh key management, etc.), users logging auth can basic stuff update address or phone number.

i want set app uses same authentication auth. if user tries access app without being logged in, want redirect them auth can log in, go page trying access on app. basically, want devise actions on app, devise residing on auth. this, of course, when have multiple sites running, can implement devise once instead of having put on every 1 of our sites individually.

i found doesn't it's quite want:

http://4trabes.com/2012/10/31/remote-authentication-with-devise/

anybody have pointer resource can walk me through how this?

thanks.

what create small api user management. allow other apps make calls api log user in, create user, etc. keeping them on whatever site they're on, in background you're talking auth api.