Slapd authenticating with krb5 localhost principal

[Jaap Winius <jwinius@umrk.nl>]

Hi folks,

My new Debian stretch slapd consumer configuration is suffering from a  
Kerberos authentication problem that looks like a bug. It is  
apparently unable to read the Kerberos keytab file and instead  
authenticates to its provider as (for my realm)  
ldap/localhost@EXAMPLE.COM. The error I keep getting is:

  slapd[1668]: GSSAPI Error: Unspecified GSS failure. \
  Minor code may provide more information \
  (Server ldap/localhost@EXAMPLE.COM not found in Kerberos database)

The software I'm using is:
* Debian stretch
* MIT Kerberos 1.15-1
* slapd 2.4.44+dfsg-3
* libsasl2-modules-gssapi-mit 2.1.27~101-g0780600+dfsg-3

The usual way to get slapd to use a Kerberos principal to authenticate  
to a provider is by telling it where the Kerberos key table file is.  
On Debian systems, slapd looks in a default location first  
(/etc/krb5.keytab), but an alternate keytab can be set in  
/etc/default/slapd with e.g.:

  export KRB5_KTNAME=/etc/ldap/krb5-ldap.keytab

Just ensure that the openldap group can read the keytab file. This  
works on Debian wheezy with slapd 2.4.31-2+deb7u2, but for some reason  
it's not working at all on Debian stretch.

Other things I have checked are:
* /etc/hostname
* hostnamectl status
* /etc/hosts (contains only '127.0.0.1 localhost' and linklocal addresses)
* DNS forward and reverse lookups

So, is this a slapd problem, or maybe something to do with a  
SASL/GSSAPI library, such as libsasl2-modules-gssapi-mit?

Thanks,

Jaap