My first time putting tacacs on a Brocade. Pretty similar to cisco, the tac pairs that cisco use seem to work just fine. Worked great with do_auth. Keep in mind, although they honor priv-15, they map it to 0, just to be different. I used the following:

username admin password yer_password_here
ip tacacs source-interface loopback 1
tacacs-server retransmit 2
tacacs-server timeout 2
tacacs-server host yer_host_here
tacacs-server key yer_key_here
enable super-user-password again_password_here
aaa authentication login default tacacs+ enable
aaa authentication login privilege-mode
aaa authentication enable default tacacs+ enable
aaa authorization commands 0 default tacacs+ none
aaa authorization exec default tacacs+
aaa accounting commands 0 default start-stop tacacs+
aaa accounting exec default start-stop tacacs+
enable aaa console