Mimic fail2ban with pf for OpenBSD.
Inspired from http://www.vincentdelft.be/post/post_20161106
In pf.conf, add according to your configuration :
table <vilain_bruteforce> persist
block quick from <vilain_bruteforce>
You might want to add a cron task to remove old banned IP. As example, to ban for one day max :
pfctl -t vilain_bruteforce -T expire 86400
To see banned IP :
pfctl -t vilain_bruteforce -T show