Rails, Node.js cross-server authentication

So I'm making a rails app that also utilizes node.js for realtime features. What is the best way to authenticate the users on the node app, if they were created with devise on rails? I've been thinking about saving the session id in the db, and then validating with that, or maybe displaying the user id in the page and then sending that to the node app when they connect. Or maybe something else entirely would be best. I'm using mongoose for my node orm and mongoid for ruby.