Unfortunatly, there is no external authentication, authorization or accounting available with the sensor software. TACACS and RADIUS can not be used. This is ironic, being a security device it still manages to fail security audits every time.
While we're on the subject of security things the sensor software can't do:
Age user passwords, force password changes, enforce minimum password requirements (it used to be you couldn't begin a password with a "$", but I havn;t tried that in 6.x) and configure the login MOTD via CSM. I'm sure I've left out a handfull, but these were on my hot list this morning.