Temporary IP Address before Authentication

I’ve been doing some reading on what appear to be old notes that detail information on configuring a mikrotik to supply a DHCP address from a temporary address pool. Once the user is authenticated they will then be supplied with an IP address from the public pool.

We are using radius manager, I know there is an option to define an IP Pool, does this come into effect after the user has authenticated?

We have had some problems where we have pre-defined the user/mac address and they havent been provided with an IP address at all.
We have Radius ticked on the DHCP server.

The idea behind this is that the user will be presented with a login page, they will enter their (provided) credentials.
This will present them with a field to enter their mac address (or do this automatically), the system will then enter their mac address into the field within their account on the radius server.

They reboot the router, automatically login as their mac address is reconised and they will be presented with a public IP.