kdc: don't allow self delegation if a backend check_constrained_delegation() hook is given
kdc: don't allow self delegation if a backend check_constrained_delegation() hook is given

A service should use S4U2Self instead of S4U2Proxy.

Windows servers allow S4U2Proxy only to explicitly configured
target principals.

metze

Signed-off-by: Love Hörnquist Åstrand <c5e2f0824a6b8bf7ea1d693b4c00a7e90e09ef7a@h5l.org>

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