gX# cat /etc/krb5.conf
[libdefaults]
        default_realm = ADX.CLASS

gX# kinit uX

[gX:~] # cat /etc/pam.d/sshd 
...
auth   sufficient      pam_krb5.so     no_warn try_first_pass
auth   required        pam_unix.so     no_warn try_first_pass
...

root@gX:~# apt-get install libpam-heimdal

root@gX:~# cat /etc/pam.d/sshd
...
auth     sufficient      pam_krb5.so
# Standard Un*x authentication.
...