When using keyed checksum types with TGS subkeys, Microsoft AD 2003

When using keyed checksum types with TGS subkeys, Microsoft AD 2003
verifies the checksum using the subkey, whereas MIT and Heimdal verify
it using the TGS session key.  (RFC 4120 is actually silent on which
is correct; RFC 4757 specifies the TGS session key.)  To sidestep this
interop issue, don't use keyed checksum types with RC4 keys without
explicit configuration in krb5.conf.  Using keyed checksum types with
AES is fine since, experimentally, AD 2008 accepts checksums keyed
with the TGS session key.

ticket: 6490
status: open
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22356 dc483132-0cff-0310-8789-dd5450dbe970