implement event triggers 'client-connect' / 'client-disconnect' to match legacy url-auth
<option name="listener_add" value="http://auth.example.org/listener_joined.php"/>
<option name="listener_remove" value="http://auth.example.org/listener_left.php"/>should translate to triggers:
- 'client-connect'
- 'client-disconnect'
Enables e.g. statistics collection without the potential problems of setting it up as auth.