Yes, progressive limits using auth. Very nice. Anyways, I just pushed AUTH support to grain. The limit configurations would be up to the relay operator. There is an example config here: 
https://github.com/0ceanSlim/grain/blob/main/app%2Fstatic%2Fexamples%2Fconfig.example.yml 

 Nice, yes, you can turn most of these into the LIMIT record and send it to the client.