How block walled garden if user doesn't open hotspot login page? [hotspot]

Hi all! I use hotspot for auth users via facebook. For it I need add facebook to walled garden (hospot login page redirect user to facebook login page with callback). Hotspot auth page located on remote server.
User connect to wifi and redirect to http://www.example.com/login?dst=

But if user not auth it can use facebook.
I can’t block all facebook pages except login, while facebook use https.
But maybe I can allow walled garden for unauth users only if them open hotpot auth page?

I.e. for user by default blocked any url except example.com (my server), if user open page on example.com - we allow walled garden for it.

Hello,
The same doubt here.
User can use Facebook mobile app without auth. Without any restrictions and out of our control.

Any news?