The interest of the firesendid utility is limited, unless you hook it to a service already providing authentication for users on your network. The Samba server does exactly that. Once a user is logged to your Samba server, you can retrieve his IP number and you can trust the authentication (the user provided a password).
To hook firesendid, you modify one share configuration (homes for one) and place a "root-preexec" directive. Using the %U and %I macro, you can update your firewall in real time from your Samba server:
[homes] . . root-preexec = /usr/lib/linuxconf/lib/firesendid --fhost host \ --port 999 --id your_server login %U %I root-postexec = /usr/lib/linuxconf/lib/firesendid --fhost host \ --port 999 --id your_server logout %U . .