This policy allows to specify the maximum age of an authentication
with which a password may be changed without re-authentication.
Defaults to 300 seconds (default taken from Constants.KC_ACTION_MAX_AGE) to remain backwards compatible.
A value of 0 will always require reauthentication to update the password.
Add documentation for MaxAuthAgePasswordPolicy to server_admin
Fixes#12943
Signed-off-by: Thomas Darimont <thomas.darimont@googlemail.com>