samba - Aug 2016 - kerberized nfs4 homedir and local account access (www-data)

Hi,

I'm stuck since one week on how to give access on a kerberized nfs4 
share to client-side local account (more precisely www-data account)...

My client setup and step-by-step configuration :
- Installed OS : XUbuntu 16.04 x64


1. Installing Samba4 from repos
2. Configuring Samba :
My client-side smb.conf :

[global]
      netbios name = TEMPOINST
      workgroup = WKG
      security = ADS
      realm = DOMAIN
      encrypt passwords = yes

      log level = 3
      log file = /var/log/samba/log.%m

      idmap config *:backend = tdb
      idmap config *:range = 70000-80000
      idmap config DPTINFO:backend = ad
      idmap config DPTINFO:schema = rfc2307
      idmap config DPTINFO:range = 10000-60000

      winbind nss info = rfc2307
      winbind trusted domains only = no
      winbind use default domain = yes
      winbind enum users  = yes
      winbind enum groups = yes

      kerberos method = system keytab

Here, DOMAIN represents the host's FQDN

3. Joining client by : "ads net join createupn=TEMPOINST\$@DOMAIN -U 
Administrator"

4. Installing Winbind and configuring accordingly nsswitch.conf (all 
wbinfo and getent are working fine)

5. Installing kerberos client and pam module to authenticate users 
against Kerberos

6. Configuring kerberos client
My client side krb5.conf

[libdefaults]
	default_realm = DOMAIN
	dns_lookup_realm = false
	dns_lookup_kdc = true

[domain_realm]
           .domain = DOMAIN
           domain = DOMAIN

[appdefaults]
     pam = {
       forwardable = true
       minimum_uid = 10000
       ignore_k5login = true
       ticket_lifetime = 1d0h0m
       debug = false
       ccache = FILE:/tmp/krb5cc_%u
     }

7. Generating krb5.keytab file by : "net ads keytab create"

8. Mounting nfs4 share with sec=krb5 option

All work fine, a domain user can log on the computer and receive a 
kerberos ticket at login. The user can use the share, permissions are 
fine too and UID,GID mapping is OK too.

But, for educational purpose I need to install  on each client a 
localhost-only apache server (with php support) which use userdir module 
to access to the 'public_html' directory into the homedir of each user. 
The problem is that local www-data user can acces the NFS share (like 
root user too).

I've tried the following :

1. Adding SPN : net ads keytab add HTTP
2. Modifying server-side idmapd.conf :
[General]

Verbosity = 5
Pipefs-Directory = /run/rpc_pipefs
Domain = domain
Local-Realms = DOMAIN

[Mapping]

Nobody-User = nobody
Nobody-Group = nogroup

[Translation]
GSS-Methods = static,nsswitch

[Static]
TEMPOINST$@DOMAIN = root
HTTP/tempoinst.domain at DOMAIN = www-data

But client-side www-data user can't access NFS share.... and the static 
for root doesn't work too 'cause "kinit TEMPOINST$" need an
unknown
password.....

All ideas would be appreciated !

Thanks by advance,
Regards,
Bruno

-- 

Bruno MACADRE
-------------------------------------------------------------------
    Ingénieur Systèmes et Réseau     | Systems and Network Engineer
    Département Informatique         | Department of computer science
    Responsable Info SER             | SER IT Manager
    Université de Rouen              | University of Rouen
-------------------------------------------------------------------
Coordonnées / Contact :
	Université de Rouen
	Faculté des Sciences et Techniques - Madrillet
	Avenue de l'Université
	CS 70012
	76801 St Etienne du Rouvray CEDEX
	FRANCE

	Tél : +33 (0)2-32-95-51-86
	Mob : +33 (0)6-74-71-45-64
-------------------------------------------------------------------


-- 

Bruno MACADRE
-------------------------------------------------------------------
  Ingénieur Systèmes et Réseau     | Systems and Network Engineer
  Département Informatique         | Department of computer science
  Responsable Info SER             | SER IT Manager
  Université de Rouen              | University of Rouen
-------------------------------------------------------------------
Coordonnées / Contact :
	Université de Rouen
	Faculté des Sciences et Techniques - Madrillet
	Avenue de l'Université
	CS 70012
	76801 St Etienne du Rouvray CEDEX
	FRANCE

	Tél : +33 (0)2-32-95-51-86
	Mob : +33 (0)6-74-71-45-64
-------------------------------------------------------------------