* allow a specific set of credentials
* reject a certain type of credentials
* deny password that can be easily cracked
* enforce use of an expiration date with a minimum of day for a password
* define a password reuse policy
* define the number of authentication failure allowed before a user is banned
* define a delay on authentication failures
* force users to change their password after first login
* throw a warning N days before when the password user is about to expire

- Fix security issue with `ALTER ROLE current_role` that allow to change
superusers password.
- Fix event trigger for password expiration warning when time diff are
negative values.
- Disable the login event trigger when `credcheck.password_valid_warning`
is not defined or set to 0.