sssd events (e.g. logins using e.g. ssh + Kerberos, or using sudo, etc.) log a
bunch of extraneous messages like this:
====
Sep 07 18:24:58 leap15-ay sssd_be[687]: GSSAPI client step 1
Sep 07 18:24:58 leap15-ay sssd_be[687]: GSSAPI client step 1
Sep 07 18:24:58 leap15-ay sssd_be[687]: GSSAPI client step 1
Sep 07 18:24:58 leap15-ay sssd_be[687]: GSSAPI client step 2
====

This was an old problem, which was previously traced to cyrus-sasl rather than
sssd itself.  It was fixed in Leap 42.3/SLE 12 with this update (taken from the
RPM changelog for cyrus-sasl):
====
* Tue Jul 25 2017 varkoly@suse.com
- bnc#1044840 syslog is polluted with messages "GSSAPI client step 1"
  By server context the connection will be sent to the log function.
  Client content does not have log level information. I.e. there is no
  way to stop DEBUG level logs nece I've removed it.
====

However the Leap 15.0 cyrus-sasl package lacks this changelog entry, which
explains the return of those annoying messages.  Unfortunately bnc#1044840 is
marked private so I can't see it, hence my filing this new one for Leap/SLE
15...