@wallabybob:
In pfSense version 2.1 snapshot builds the User Manager (System -> User Manager in web GUI) allows users to be assigned to groups and there is a group permission for "Login to captive portal".
So it would appear you can accomplish what you describe by using "local authentication" in captive portal.
I haven't tried this and I haven't checked availability in pfSense 2.0.x builds.
I try this method (local authentication) and also Radius server (internal and external), it worked very well BUT there is NO WAY to disable a group of users to access internet at the same time.
It appears that it must be done one-by-one, and for my needs it's a mess.
I wish to disable/enable internet access to a group of 20/30 users at the same time…
It seems no possible with pfsense.
[UPDATE]: I realize that this function is added in pfsense v. 2.1 beta.
You can choose at group (or user) level if the user/group can authenticate to Captive Portal.