[Dovecot] AD Kerberos and Dovecot

Hello,

I got stucked on Kerberos auth with Dovecot:

Jan 22 17:48:36 test dovecot: auth: Error: LDAP: binding failed (dn cn=AUTH\_ldap): Local error, SASL(-1): generic failure: GSSAPI Error: Unspecified GSS failure. Minor code may provide more information (Credentials cache file '/tmp/krb5cc_1003' not found)

kinit and and ldapsearch with gssapi auth are working.

Are there instructions how to set up Kerberos auth with Dovecot and Active Directory? How does Dovecot handle Kerberos tickets?

best regards Christian