[Samba] Access to NFSv4 Filesystem

[rfs]

Hi,

i've been spending quite some time on figuring out how to setup samba to
access user data on a NFSv4 share that is secured by kerberos. User home
directories reside on this network filesystem.

kdc01.fqdn:/users/ on /home type nfs4
(rw,sec=krb5,addr=w.x.y.1,clientaddr=w.x.y.2)

setting up samba for kerberos, i followed these descriptions:
   https://help.ubuntu.com/community/Samba/Kerberos

security setting: "security = user"
(i checked out the ads setup, too, but with the same result)

My current setup is working when 'kerberos security' is switched off for
the NFSv4 mount. Therefore i think kerberos authentication is working.
The Problem is: Samba should open a pam session, getting a kerberos
ticket for the user to access the data.

Which configuration steps are required to accomplish this? Or is it
totally insane to do that?
I did not want to setup an Samba share on the actual File Server. Is
this the only way to do that?

Cheers,
rfs