[Samba] samba 4 PAM and xscreensaver

[steve]

Hi
I have a Linux client running XFCE and authenticating against Samba 4. 
When trying to return to the session after xscreensaver has kicked in, 
authentication fails.

/etc/pam.d/xscreensaver
#%PAM-1.0
auth     include        common-auth
account  include        common-account
password include        common-password
session  include        common-session

/etc/pam.d/common-password
#%PAM-1.0
password    requisite    pam_pwcheck.so    nullok cracklib
password    optional    pam_gnome_keyring.so    use_authtok
password    sufficient    pam_unix2.so    use_authtok nullok
password    required    pam_ldap.so    try_first_pass use_authtok

Samba 4 seems to bypass pam, users have an entry in the keytab on the 
Samba 4 server and this on the client:
/etc/krb5.conf
[libdefaults]
     default_realm = HH3.SITE
     dns_lookup_realm = false
     dns_lookup_kdc = true


How can I tell xscreensaver to authenticate against Samba 4?
Thanks
Steve