Using the Active Directory users’ kerberos credential cache file from inside a docker container

After an Active Directory user logins to a docker container, the kerberos credential cache file (krb5cc_<uid>, or krb5cc_cdc<unique_number>_<uid>) is created in /tmp in the CoreOS host, not in /tmp in the docker container.

The workaround (for now) is for the docker container to mount the
/tmp directory using "-v /tmp:/tmp" in the docker run command.