I figured out the problem. My
krb5.keytab file somehow got corrupted on my OpenLDAP server. I
just needed to deleted it and recreate it. I got tipped off to
the problem when I started having login issues to the server as
well.
FWIW: There's a contrib overlay to achieve this without having to use SASL pass-through. See directory contrib/slapd-modules/kinit/ in the source tree. Not sure which status this has though. Ciao, Michael.