Rb450 and routerOs

I have a rb450 → captive portal → cable modem

Rb450 serves dhcp 192.168.205.1-254 wan port 192.168.10.9
Captive portal 192.168.10.8 wan port public ip

When a client connects the captive portal sees the 192.168.10.9 address and mac of router.
First person logs in and everyone after gets a free ride.

How can I setup the rb450 so that the captive portal gets a unique identifier for every client?

Work you with NAT on the router?

How have you configured the router?