>Active Directory is Microsoft's proprietary tech that is a modification of the Kerberos standard
And LDAP, and some DNS, and certs, etc. It's not just Kerberos; you're sounding ignorant here.
>Group permissions predate AD by decades
No one said otherwise, but it goes beyond basic POSIX groups with things like nested groups, delegated group permissions, etc.
>SSO in today's form is a web phenomenon
So is AD's...
Basically, you're proving my point.