Problem with configuration of Kerberos Auth with Docker (or Linux)

While the documentation of configuring authentication with Kerberos for IRIS on Linux servers is sparse, for docker i found no docs at all. Assuming I would be able to adapt the requirements from linux to docker (on linux host) I had no success at all. Has anyone successfully done this?

Even with "do ^REDEBUG" set to FFFFFFFF the log did not help much, I always get "Kerberos error getting initial credentials with password; KDC reply did not match expectations". Since I moved the iris.keytab-file to different locations and always get the same error I assume, it is not reckognized by IRIS (Permissions are 640 and the owner: group is 51773:52773).

Can anyone give me a hint? Would be much appreciated!