Logging from other plugins

[wp-fail2ban]

Continuing the discussion from Blocking Empty Usernames:

@Andy

Is there any possibility to use a hook or action, that I can use in other plugins, to trigger a WPfail2ban log to the auth.log?
I also use iThemesSecurityPro - and I would like just to add a fail2ban log to some parts of the plugin - as the only real blocking for me is on iptables layer, not on application layer.

That depends on exactly what you mean

You can already register custom messages for plugins:
Docs: Example code
Example: Add-on - Contact Form 7
Example: Add-on - Gravity Forms

However, if you’re trying to simulate a particular event there’s currently no mechanism for that.