Client Authentication:Debian via sssd/ldap

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Warning.png Warning:
This how-to should be validated by Daniel before you use it!!.


Warning.png Warning:
This is based upon limited testing and a small number of users.

Introduction

This how-to shows how to configure a SME-server (>=8b6) and a client Debian (method tested with Debian squeeze) for a LDAP based SSSD authentication of the client machine on the configured user accounts of the SME.

The main advantage in comparaison to nss_ldap is that the authentication informations stay in the cache and the authentication can therefore further work, even in offline mode (when the server not available).

Nevertheless, the creation of a local user with the admin rights is recommanded for the emergency case.

These lines are a translation of the method given by Daniel: https://wikit.firewall-services.com/doku.php/tuto/ipasserelle/authentification/debian_sssd_on_sme. Many thanks to him for it.

In this how-to: we assume that:

the host name of the SME is "sme-server" and the domain is "domain.tld".

Configuration of the SME-server

There is quite no necessary configuration of the SME.

  • The only thing to do is to create a user (named "auth" in this how-to) via the server-manager and to give him a valid password ("something_very_secret" in the how-to).

It is not required to make "auth" member of any group.

  • In addition, it is recommended to install and configure PHPki in order to make the managing of the self-created certificates easier.


Configuration of the client Debian

Manage the CA of the SME

after having installed PHPki, go to https://www.domain.tld/phpki and download on the client machine the certificate of authority (ca-certificates.crt).

Place a copy of it or of another CA into /etc/ssl/certs/ and give the 644 permissions:

cp ~/download/ca-certificates.crt /etc/ssl/certs/
chmod 644 /etc/ssl/certs/ca-certificates.crt

Install the required packages

apt-get install sssd libnss-sss libpam-sss ca-certificates

Configure sssd

The configuration is made by the file /ets/sssd/sssd.conf.

  • At the beginning of this file, the used domain has to be set. In sssd, a domain can be taken as a source of content. it is possible to set several domains in order of priority.
  • And deeper in the file, we will add the configuration of the domain


If the file doesn't exist by default it has to be created and it needs to get the permissions 600 to allow the daemon to start: cat <<'_EOF' > /etc/sssd/sssd.conf

[sssd]
config_file_version = 2
services = nss, pam
domains = LDAP

[nss]

[pam]

[domain/LDAP]
id_provider = ldap
auth_provider = ldap
ldap_schema = rfc2307
ldap_uri = ldap://sme-server.domain.tld
ldap_default_bind_dn = uid=auth,ou=Users,dc=domain,dc=tld
ldap_default_authtok = something_very_secret
ldap_default_authtok_type = password
ldap_search_base = dc=domain,dc=tld
ldap_user_search_base = ou=Users,dc=domain,dc=tld
ldap_group_search_base = ou=Groups,dc=domain,dc=tld
ldap_user_object_class = inetOrgPerson
ldap_user_gecos = cn
ldap_tls_reqcert = hard
ldap_tls_cacert = /etc/ssl/certs/ca-certificates.crt
ldap_id_use_start_tls = true
# uncomment below if the SME is a “iPasserelle”
#ldap_user_shell = desktopLoginShell
# comment below if the SME is a “iPasserelle”
override_shell = /bin/bash
cache_credentials = true
enumerate = true
# It is possible to filter the logins via a LDAP-filer
# by commenting the both lines below.
# In this exemple, only the users member of the group netusers
# will be valid on this host.
# posixMemberOF is a parameter only for a iPasserelle
#access_provider = ldap
#ldap_access_filter = (|(posixMemberOf=admins)(uid=backup))
_EOF

chmod 600 /etc/sssd/sssd.conf


Information.png Tip:
Make sure that the file /etc/ssl/certs/ca-certificates.crt contains the CA that has sign the certificate of the SME (if PHPki is used, a version > 0,82-13 is required).


nsswitch

Edit /etc/nsswitch.conf and add sss for passwd, group and shadow:

passwd:         compat sss
group:          compat sss
shadow:         compat sss

pam

cd /etc/pam.d
cp -a common-account common-account.orig
cat <<'EOF'> common-account
#
# /etc/pam.d/common-account - authorization settings common to all services
#
account [success=1 new_authtok_reqd=done default=ignore]  pam_unix.so
# here's the fallback if no module succeeds
account requisite                       pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
account required                        pam_permit.so
# and here are more per-package modules (the "Additional" block)
session optional      pam_mkhomedir.so skel=/etc/skel umask=0077
account [default=bad success=ok user_unknown=ignore]    pam_sss.so
EOF

cp -a common-auth common-auth.orig
cat <<'EOF'> common-auth
#
# /etc/pam.d/common-auth - authentication settings common to all services
#
# here are the per-package modules (the "Primary" block)
auth    [success=2 default=ignore]                      pam_sss.so
auth    [success=1 default=ignore]      pam_unix.so nullok_secure try_first_pass
# here's the fallback if no module succeeds
auth    requisite                       pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
auth    required                        pam_permit.so
# and here are more per-package modules (the "Additional" block)
EOF

cp -a common-password common-password.orig
cat <<'EOF'> common-password
#
# /etc/pam.d/common-password - password-related modules common to all services
# here are the per-package modules (the "Primary" block)
password        sufficient                      pam_sss.so
password        [success=1 default=ignore]      pam_unix.so obscure try_first_pass sha512
# here's the fallback if no module succeeds
password        requisite                       pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
password        required                        pam_permit.so
# and here are more per-package modules (the "Additional" block)
EOF

cp -a common-session common-session.orig
cat <<'EOF'> common-session
#
# /etc/pam.d/common-session - session-related modules common to all services
# 
# here are the per-package modules (the "Primary" block)
session [default=1]   pam_permit.so
# here's the fallback if no module succeeds
session requisite     pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
session required      pam_permit.so
# and here are more per-package modules (the "Additional" block)
session optional      pam_mkhomedir.so skel=/etc/skel umask=0077
session optional      pam_sss.so
session required      pam_unix.so 
EOF

Enable at statup

update-rc.d sssd enable
/etc/init.d/sssd start