KDB: support external IdP configuration
When IdP configuration is provided, take it into account:
- idp-specific Kerberos ticket policy would be applied
- Presence of IdP link in a Kerberos principal entry would cause KDB to
enable `idp` pre-authentication method on KDC side.
The latter requires additional pre-authentication method supplied with
SSSD 2.7.0.
Fixes: https://pagure.io/freeipa/issue/8804
Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
Signed-off-by: Pavel Březina <pbrezina@redhat.com>
Reviewed-By: Francisco Trivino <ftrivino@redhat.com>
Reviewed-By: Sumit Bose <sbose@redhat.com>