New in version 3.0.0.
This is for some flavours of Linux where WP_FAIL2BAN_SYSLOG_SHORT_TAG isn’t enough.
If you configure your web server to set an environment variable named WP_FAIL2BAN_SYSLOG_SHORT_TAG on a per-virtual host basis, WPf2b will use that in the syslog tag. This allows you to configure a unique tag per site in a way that makes sense for your configuration, rather than some arbitrary truncation or hashing within the plugin.
This feature has not been tested as extensively as others. While I’m confident it works, FreeBSD doesn’t have this problem so this feature will always be second-tier.