Access backend Node JS application from Rails + NGINX

Question

So I have a NGINX Webserver forwarding connections from port 80 to my Rails application. The Rails application handles authentication and serves basic functionality and static pages. I have several local apps on various internal ports that I would like to link to after the user has authenticated. I could open these ports externally but that would defeat the purpose of authentication.

Can someone point me in the direction to have this work the way I want it?

Thanks in advance