one of the documented procedures in this installation of the ACS
address_book_authorized   scope   db   { group_id "0" }
What it does:
If scope=0, return 1 if the user is authorized; 0 otherwise. Otherwise, returns 1. This function will expand as we expand the permissions in the address book
Defined in: /web/philip/tcl/address-book-defs.tcl

Source code:

    # user should be in the group 
    if {$scope=="group" && ![ad_user_group_member $db $group_id]} {
	return 0
    } else {
	return 1