Authorising with Node, serving with Nginx

I expect this question has been answered, but because I'm unsure of the terminology I might have missed, or not understood the answer.

I would like to use Nodejs to authorise and parse a GET request, i.e:

something.com/app/?key=12345&files=all

Then once this is read by node, key authorised, and the files requested compiled, node would tell Nginx to serve back some static files based on this request.

• So, is this possible?
• Is there a better way of doing this (I have seen a lot about serving static files with Nginx instead of Nodejs)

edit - Just to inform, i'm using Express, routing is not my problem. Its just I don't know how to pass a successful request back to Nginx, or something like that