Watchguard - passwordless SSH login to block/ban IP addresses

I have Watchguard XTM22-W as my firewall. On it there are few 1-to-1 NAT policies through which I access local services (mainly SSH on different machines). All these machines have Fail2Ban installed and send everything to a central log server. All machines run Ubuntu and use rsyslog.

As I collect all addresses to be banned on one place, I would like to have a script, running on this Linux box, where I will login to the Watchguard and execute couple commands there. This way I will stop the bad traffic at the entry point.

The issue I have with this is how to make passwordless admin login for Watchguard? It doesn't seem to provide functionality for that. Another option will be to tweak it auto-block feature, so it will ban IP addresses who abuse SSH. But then - how would it know how many attempts were made?

Thanks!