Requires name, description as all other connectors. The connector just checks
the password, the role is static for all users and given as key role.
The key source must be a connector reference that supports the password
bind query syntax.
Suited connectors are e.g. Connector::Builtin::Authentication::*
label: User Password
returns a pair of (user, role, response_message) for a given login
step. If user and role are undefined, the login is not yet finished.