MIKROTIK CHR Radius server to connect with on premise Router

Good day please I Ned some help I have 2mikrotik Router.
ROUTER A is a CHR with static address Wan hosted on aws
ROUTER B is on premise with Dhcp Wan

I want a situation where by router b Hotspot checks if the username of a user is on the cloud router using radius [user manager] if the username name is on router A allow the user connect to router b and have access to internet


I Need help at the radius server and client part

Thank you.