I don't know about UserMan, but FreeRADIUS lets you do that.
Do realize that it can be a security weakness because if someone captures your RADIUS secret, they can connect to your server from that same range and start making brute force attempts on your passwords.
Maybe not ... But it better should be.MT,
I'm missing this on the RB3011:
Memory card type 1 x M.2 SDD (which can be used as bootable drive).
i think the only mikrotik with this feature is ccr1072, but dont know if can be booted from m2