[keycloak-user] Only accept some email adress, for registration?

Hello, I'm searching for a way to allow registration via the web interface from keycloak (the default one, if possible, not something I'd code myself) to be limited to certain email domains. Is it possible? If no: how do you do it in practice? Thanks, ps: still searching for a way to automatically set up profile attribute at user registration, such as a unique numerique attribute (1, 2, 3, …) for each user