LDAP Authentication

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I found this guide to be very useful as it lists answers to the debconf questions. The only difference between the recommended configuration and tardis' is that "Local crypt to use when changing passwords." should be 'exop'.

Getting user information from LDAP

The libnss-ldap package handles fetching account information from LDAP. Also make sure that nscd is installed, otherwise bad things may happen.

To tell libnss-ldap where to look, you need to edit the /etc/libnss-ldap.conf. At the very least, you'll need to give the host and base (dc=tardis,dc=ed,dc=ac,dc=uk).

To tell libc to use libnss-ldap, you need to amend the appropriate lines in /etc/nsswitch.conf:

passwd:         files ldap 
group:          files ldap
shadow:         files ldap

The other databases are best left alone; we don't bother putting host information or such like in LDAP because we don't see much benefit.

The getent program is useful for testing.

Authenticating with LDAP

The libpam-ldap package is used for authentication against LDAP. You need to configure /etc/pam_ldap.conf along the same lines as /etc/libnss_ldap.conf. A typical example is:

host piper
base dc=tardis,dc=ed,dc=ac,dc=uk
rootbinddn cn=admin,dc=tardis,dc=ed,dc=ac,dc=uk
ldap_version 3

# NSS lookups need to be restricted to the appropriate parts of the tree.
# If other lookups are added to /etc/nsswitch.conf, they need to be put
# here too.
nss_base_passwd ou=People,dc=tardis,dc=ed,dc=ac,dc=uk
nss_base_group   ou=Group,dc=tardis,dc=ed,dc=ac,dc=uk
nss_base_shadow ou=People,dc=tardis,dc=ed,dc=ac,dc=uk

# Use funky generic LDAP password changing.
pam_password exop

PAM needs to be told to use libpam-ldap, as well as the normal authentication for root. Canonical /etc/pam.d/common-auth:

# ** Use trick from /usr/share/doc/libpam-ldap/README.Debian
auth    [success=1 default=ignore]      pam_unix.so nullok_secure
auth    required                        pam_ldap.so use_first_pass
auth    required                        pam_permit.so

Note the use_first_pass option. Without it logins will ask for a password for pam_unix, then one for pam_ldap, and so on, causing every other attempt to enter your password to fail even when you get it right. You need to set up /etc/pam.d/common-account in the same way.

For Red Hat-based Distros

This guide was tested with Fedora Server 21 (on Valiant).

  • Run `authconfig-tui` (if not installed, `yum install -y authconfig`
  • Check 'Use LDAP' and 'Use LDAP Authentication'. Make sure 'Local authorization is sufficient' is also checked.
  • Leave `Use TLS` unchecked.
  • Set server to `ldap://ldap/`
  • Set Base DN to `dc=tardis,dc=ed,dc=ac,dc=uk`