SQUID ACL for Radius Authenticated users

Hi,
My hotspot setup with Radius manager, Mikotik and Squid in Transparent proxy is working fine.
I want create an ACL in squid just to allow certain list of authenticates users in the Radius Server only.

For eg: Allow users user 1, user 2, user3 only to download 20MB size file.

Can you please share your ideas on this ,

thanks,

Navas