Smart router to containers

I have some simple project that based on 2 docker containers. Containers are Apache servers - with static HTML files (without PHP).

• Container 1: Public content.
• Container 2: Private content - for registered users only.

The idea is that users enter to some link, lets say: http://ift.tt/2hV6hyn

Then I need to route them to the right container. Users have tokens in their localstorage(or cookies) - so that's way I can detect where I need to route the user.

My problem is that I can't understand how to develop that router.

The issue is that I can't change to URL - so I can't create sub domains, URL level or something like this... I need to allow to users copy urls and sends to each other.

Please take a look to the attachment image bellow, maybe it will help to understand the arch.