It easy to find if user is logged in. But how can I check if user is logged with specific oauth client?. ex. Google or Facebook
You can check with perticuler IDs and for more see here
https://scotch.io/tutorials/easy-node-authentication-setup-and-local
http://mherman.org/blog/2013/11/10/social-authentication-with-passport-dot-js/#.VjbvGVUrLIU