s4:kdc: Add KDC support for Protected Users group

s4:kdc: Add KDC support for Protected Users group

Accounts in the Protected Users group acting as clients lack support for
the RC4 encryption type. TGTs issued to such accounts have a lifetime
restricted to four hours, and are unable to be proxied or forwarded.

To determine at lookup time whether a client account is a member of
Protected Users, we now also create an auth_user_info_dc structure when
creating the database entry for an AS-REQ, rather than only when
creating a PAC for a TGT, or when recreating the PAC from an RODC-issued
TGT.

This means that the user's groups are now expanded even for AS-REQs that
result in an error (such as a PREAUTH_REQUIRED error), but this is
required to be able to correctly determine the account's available
encryption types, which are needed soon after fetching the user account.

Currently, the TGT lifetime may exceed four hours (for Heimdal
specifically). This may happen if PKINIT is used, and either the
pkinit_max_life_from_cert_extension option is TRUE and
pkinit_max_life_bound is greater than four hours, or
pkinit_max_life_from_cert is greater than four hours.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>