Client Authentication:Centos via sssd/ldap
Introduction
This how-to shows how to configure a SME-server (>=8b6) and a client Centos >= 5 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 furter 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/centos_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 CentOS
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.crt).
Place a copy of it or of another CA into /etc/phpki/tls/certs/ and give the 644 permissions:
cp ~/download/ca.crt /etc/phpki/tls/certs/ chmod 644 /etc/phpki/tls/certs/ca.crt
Install the required package
First of all, install the required package:
yum install sssd
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/pki/tls/certs/ca.crt ldap_id_use_start_tls = true # uncomment below if the SME is a âiPasserelleâ #ldap_user_shell = desktopLoginShell # comment below if the SME is a âiPasserelleâ 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
Configure nss
To allow nss to use sssd, you should check that sss is set as a source for users and groups in the /etc/nsswitch.conf.
[...] passwd: files sss shadow: files sss group: files sss [...] netgroup: files sss
Check
getent passwd
should show the ldap-users. If it doen't work, you should start debugging by running sssd in interactiv mode (with sssd -i -d 5 for exemple).
Configure pam
pam must be configured on order to use sssd as a source too:
CentOS 5
rm -f /etc/pam.d/system-auth cat <<'EOF' > /etc/pam.d/system-auth #%PAM-1.0 # This file is auto-generated. # User changes will be destroyed the next time authconfig is run. auth required pam_env.so auth sufficient pam_unix.so nullok try_first_pass auth requisite pam_succeed_if.so uid >= 500 quiet auth sufficient pam_sss.so use_first_pass auth required pam_deny.so account required pam_unix.so account sufficient pam_succeed_if.so uid < 500 quiet account [default=bad success=ok user_unknown=ignore] pam_sss.so account required pam_permit.so password requisite pam_cracklib.so try_first_pass retry=3 password sufficient pam_unix.so md5 shadow nullok try_first_pass use_authtok password sufficient pam_sss.so use_authtok password required pam_deny.so session optional pam_keyinit.so revoke session required pam_limits.so session optional pam_mkhomedir.so skel=/etc/skel umask=0077 session [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid session required pam_unix.so session optional pam_sss.so EOF
CentOS 6 / 7
rm -f /etc/pam.d/system-auth cat <<'EOF' > /etc/pam.d/system-auth #%PAM-1.0 # This file is auto-generated. # User changes will be destroyed the next time authconfig is run. auth required pam_env.so auth sufficient pam_unix.so nullok try_first_pass auth requisite pam_succeed_if.so uid >= 500 quiet auth sufficient pam_sss.so use_first_pass auth required pam_deny.so account required pam_unix.so account sufficient pam_succeed_if.so uid < 500 quiet account [default=bad success=ok user_unknown=ignore] pam_sss.so account required pam_permit.so password requisite pam_cracklib.so try_first_pass retry=3 type= password sufficient pam_unix.so sha512 shadow nullok try_first_pass use_authtok password sufficient pam_sss.so use_authtok password required pam_deny.so session optional pam_keyinit.so revoke session required pam_limits.so session optional pam_mkhomedir.so skel=/etc/skel umask=0077 session [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid session required pam_unix.so session optional pam_sss.so EOF rm -f /etc/pam.d/password-auth ln -sf system-auth /etc/pam.d/password-auth
That's all. It has only to be tested now. When it works, the daemon sssd should be enabled at start:
chkconfig sssd on
or
systemctl enable sssd
