event/4 or event/5 is called whenever an event
occurs in the mod_security Erlang web server API module.
(event/4 is called if Address is undefined,
otherwise event/5.
Argument What specifies the type of event that has
occurred and is one of the following reasons:
auth_fail
A failed user authentication.
user_block
A user is being blocked from access.
user_unblock
A user is being removed from the block list.
The event user_unblock is not triggered when
a user is removed from the block list explicitly using the
unblock_user function.