[SSSD] [sssd PR#5629][opened] KCM: return KRB5_FCC_INTERNAL for unknown or not implemented operation

[pbrezina]

   URL: https://github.com/SSSD/sssd/pull/5629
Author: pbrezina
 Title: #5629: KCM: return KRB5_FCC_INTERNAL for unknown or not implemented operation
Action: opened

PR body:
"""
sssd-kcm should follow Heimdal's return codes. Heimdal returns `KRB5_FCC_INTERNAL`
for cases where operation code is not known or not implemented. See:

* https://github.com/heimdal/heimdal/blob/master/kcm/protocol.c#L1785
* https://github.com/heimdal/heimdal/blob/master/kcm/protocol.c#L1792

We returned different codes before this patch which makes Kerberos to differentiate
between Heimdal and sssd implementation. This leads to errors like:

* https://github.com/krb5/krb5/pull/1178#issuecomment-838289703

Resolves: https://github.com/SSSD/sssd/issues/5628
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/5629/head:pr5629
git checkout pr5629