security/pam_ldap is configured via /usr/local/etc/ldap.conf.

Thus, we will want to copy all of our original configuration parameters from openldap/ldap.conf to the new ldap.conf. Once this is done, we want to tell security/pam_ldap what to look for on the directory server.

We are identifying our users with the uid attribute. To configure this (though it is the default), set the pam_login_attribute directive in ldap.conf:

pam_login_attribute uid

With this set, security/pam_ldap will search the entire LDAP directory under base for the value uid=username. If it finds one and only one entry, it will attempt to bind as that user with the password it was given. If it binds correctly, then it will allow access. Otherwise it will fail.

Users whose shell is not in /etc/shells will not be able to log in. This is particularly important when Bash is set as the user shell on the LDAP server. Bash is not included with a default installation of FreeBSD. When installed from a package or port, it is located at /usr/local/bin/bash. Verify that the path to the shell on the server is set correctly:

% getent passwd username

There are two choices when the output shows /bin/bash in the last column. The first is to change the user's entry on the LDAP server to /usr/local/bin/bash. The second option is to create a symlink on the LDAP client computer so Bash is found at the correct location:

# ln -s /usr/local/bin/bash /bin/bash

Make sure that /etc/shells contains entries for both /usr/local/bin/bash and /bin/bash. The user will then be able to log in to the system with Bash as their shell.

auth  sufficient  /usr/local/lib/pam_ldap.so  no_warn

pam_groupdn cn=servername,ou=accessgroups,dc=example,dc=org

memberUid: uid=someuser,ou=people,dc=example,dc=org

auth            required        pam_nologin.so          no_warn
auth            sufficient      pam_opie.so             no_warn no_fake_prompts
auth            requisite       pam_opieaccess.so       no_warn allow_local
auth            sufficient      /usr/local/lib/pam_ldap.so      no_warn
auth            required        pam_unix.so             no_warn try_first_pass

account         required        pam_login_access.so
account         required        /usr/local/lib/pam_ldap.so      no_warn ignore_authinfo_unavail ignore_unknown_user

NSS is the service that maps attributes to names. So, for example, if a file is owned by user 1001, an application will query NSS for the name of 1001, and it might get bob or ted or whatever the user's name is.

Now that our user information is kept in LDAP, we need to tell NSS to look there when queried.

The net/nss_ldap port does this. It uses the same configuration file as security/pam_ldap, and should not need any extra parameters once it is installed. Instead, what is left is simply to edit /etc/nsswitch.conf to take advantage of the directory. Simply replace the following lines:

group: compat
passwd: compat

with

group: files ldap
passwd: files ldap

This will allow you to map usernames to UIDs and UIDs to usernames.

Congratulations! You should now have working LDAP authentication.

Unfortunately, as of the time this was written FreeBSD did not support changing user passwords with passwd(1). As a result of this, most administrators are left to implement a solution themselves. I provide some examples here. Note that if you write your own password change script, there are some security issues you should be made aware of; see Section 4.3, “Password Storage”

#!/bin/sh

stty -echo
read -p "Old Password: " oldp; echo
read -p "New Password: " np1; echo
read -p "Retype New Password: " np2; echo
stty echo

if [ "$np1" != "$np2" ]; then
  echo "Passwords do not match."
  exit 1
fi

ldappasswd -D uid="$USER",ou=people,dc=example,dc=org \
  -w "$oldp" \
  -a "$oldp" \
  -s "$np1"

# sysctl security.bsd.see_other_uids=0

A more flexible (and probably more secure) approach can be used by writing a custom program, or even a web interface. The following is part of a Ruby library that can change LDAP passwords. It sees use both on the command line, and on the web.

require 'ldap'
require 'base64'
require 'digest'
require 'password' # ruby-password

ldap_server = "ldap.example.org"
luser = "uid=#{ENV['USER']},ou=people,dc=example,dc=org"

# get the new password, check it, and create a salted hash from it
def get_password
  pwd1 = Password.get("New Password: ")
  pwd2 = Password.get("Retype New Password: ")

  raise if pwd1 != pwd2
  pwd1.check # check password strength

  salt = rand.to_s.gsub(/0\./, '')
  pass = pwd1.to_s
  hash = "{SSHA}"+Base64.encode64(Digest::SHA1.digest("#{pass}#{salt}")+salt).chomp!
  return hash
end

oldp = Password.get("Old Password: ")
newp = get_password

# We'll just replace it.  That we can bind proves that we either know
# the old password or are an admin.

replace = LDAP::Mod.new(LDAP::LDAP_MOD_REPLACE | LDAP::LDAP_MOD_BVALUES,
                        "userPassword",
                        [newp])

conn = LDAP::SSLConn.new(ldap_server, 389, true)
conn.set_option(LDAP::LDAP_OPT_PROTOCOL_VERSION, 3)
conn.bind(luser, oldp)
conn.modify(luser, [replace])

Although not guaranteed to be free of security holes (the password is kept in memory, for example) this is cleaner and more flexible than a simple sh script.