Captive Portal Pre-Login Customization

Hello, I offer captive portal solutions. I currently use a platform that has custom splash pages, authenticates users and has a good emaling tool within the platform. I client is asking for something that goes beyond what my platform offers. I need to integrate a Pre-login page that will validate a code for users prior to logging in on the usual login page. You will find the detail in the attached file.

I would prefer to use a Mikrotik or Aruba Instan On solution for this.

Please contact me if this is something that you could do.