What would you like to be added or enhanced?

For all database password-based authentication integrations, add selected columns as client_attrs, similar to the approach used in HTTP authentication.

For example:

SELECT password_hash, salt, is_superuser, sn as client_attrs.sn FROM mqtt_user WHERE username = ${username} LIMIT 1

Why is this needed?

This expands the authentication possibilities to the same level as HTTP authentication, without the need for an external authentication service/endpoint.