This optional parameter, in conjunction with CheckGroup,
allows you to set a Class reply attribute that depends on which NT group
the user is a member of. CheckGroupServer is the name of an NT domain
controller that contains group information.
<AuthBy ADSI>
CheckGroupServer brbaaa01
CheckGroup USVPN,ou=tcgic
CheckGroup UKVPN,ou=tcgic
....
</AuthBy>