Difference between revisions of "LDAP authentication"

Revision as of 22:09, 12 January 2014

Introduction and Concepts

This is a guide on how to configure an Arch Linux installation to authenticate against an LDAP directory. This LDAP directory can be either local (installed on the same computer) or network (e.g. in a lab environment where central authentication is desired).

The guide is divided into two parts. The first part deals with how to setup an OpenLDAP server that hosts the authentication directory. The second part deals with how to setup the NSS and PAM modules that are required for the authentication scheme to work on the client computers. If you just want to configure Arch to authenticate against an already existing LDAP server, you can skip to the second part.

NSS and PAM

NSS (which stands for Name Service Switch) is a system mechanism to configure different sources for common configuration databases. For example, /etc/passwd is a file type source for the passwd database.

PAM (which stands for Pluggable Authentication Module) is a mechanism used by Linux (and most *nixes) to extend its authentication schemes based on different plugins.

So to summarize, we need to configure NSS to use the OpenLDAP server as a source for the passwd, shadow and other configuration databases and then configure PAM to use these sources to authenticate it's users.

LDAP Server Setup

Installation

You can read about installation and basic configuration in the OpenLDAP article. After you have completed that, return here.

Set up access controls

To make sure that no-one can read the (encrypted) passwords from the LDAP server, but a user can edit their own password, add the following to /etc/openldap/slapd.conf and restart slapd.service afterwards:

slapd.conf

access to attrs=userPassword
        by self write
        by anonymous auth
        by * none

access to *
        by self write
        by * read

Populate LDAP Tree with Base Data

Create a temporarily file called base.ldif with the following text.

Note: If you have a different domain name then alter "example" and "org" to your needs

base.ldif

# example.org
dn: dc=example,dc=org
dc: example
o: Example Organization
objectClass: dcObject
objectClass: organization

# Manager, example.org
dn: cn=Manager,dc=example,dc=org
cn: Manager
description: LDAP administrator
objectClass: organizationalRole
objectClass: top
roleOccupant: dc=example,dc=org

# People, example.org
dn: ou=People,dc=example,dc=org
ou: People
objectClass: top
objectClass: organizationalUnit

# Groups, example.org
dn: ou=Groups,dc=example,dc=org
ou: Groups
objectClass: top
objectClass: organizationalUnit

Add it to your OpenLDAP Tree:

$ ldapadd -D "cn=Manager,dc=example,dc=org" -W -f base.ldif

Test to make sure the data was imported:

$ ldapsearch -x -b 'dc=example,dc=org' '(objectclass=*)'

Adding users

To manually add a user, create an .ldif file like this:

user_joe.ldif

dn: uid=johndoe,ou=People,dc=example,dc=org
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
uid: johndoe
cn: John Doe
sn: Doe
givenName: John
title: Guinea Pig
telephoneNumber: +0 000 000 0000
mobile: +0 000 000 0000
postalAddress: AddressLine1$AddressLine2$AddressLine3
userPassword: {CRYPT}xxxxxxxxxx
labeledURI: https://archlinux.org/
loginShell: /bin/bash
uidNumber: 9999
gidNumber: 9999
homeDirectory: /home/johndoe/
description: This is an example user

The xxxxxxxxxx in the userPassword entry should be replaced with the value in /etc/shadow or use the slappasswd command. Now add the user:

$ ldapadd -D "cn=Manager,dc=example,dc=org" -W -f user_joe.ldif

Note: You can automatically migrate all of your local accounts (and groups, etc.) to the LDAP directory using PADL Software's Migration Tools.

Client Setup

Install the OpenLDAP client as described in OpenLDAP. Make sure you can query the server with ldapsearch.

Next, install nss-pam-ldapd^AUR from the official repositories.

NSS Configuration

NSS is a system facility which manages different sources as configuration databases. For example, /etc/passwd is a file type source for the passwd database, which stores the user accounts.

Edit /etc/nsswitch.conf which is the central configuration file for NSS. It tells NSS which sources to use for which system databases. We need to add the ldap directive to the passwd, group and shadow databases, so be sure your file looks like this:

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

Edit /etc/nslcd.conf and change the base and uri lines to fit your ldap server setup.

Start nslcd.service using systemd.

You now should see your LDAP users when running getent passwd on the client.

Name Service Cache Daemon

You can optionally run NSCD. This is a daemon that NSS uses to cache lookups and queries for network backends. This way you can login when the LDAP server is down, it will also reduce load on the LDAP server.

Start nscd.service using systemd.

Note: It is recommended to stop the NSCD when troubleshooting because it may mask problems by serving cached queries.

PAM Configuration

The basic rule of thumb for PAM configuration is to include pam_ldap.so wherever pam_unix.so is included. Arch moving to pambase has helped decrease the amount of edits required. For more details about configuring pam, the RedHat Documentation is quite good. You might also want the upstream documentation for nss-pam-ldapd.

Tip: If you want to prevent UID clashes with local users on your system, you might want to include minimum_uid=10000 or similar on the end of the pam_ldap.so lines. You'll have to make sure the LDAP server returns uidNumber fields that match the restriction.

Note: Each facility (auth, session, password, account) forms a separate chain and the order matters. Sufficient lines will sometimes "short circuit" and skip the rest of the section, so the rule of thumb for auth, password, and account is sufficient lines before required, but after required lines for the session section; optional can almost always go at the end. When adding your pam_ldap.so lines, don't change the relative order of the other lines without good reason! Simply insert LDAP within the chain.

First edit /etc/pam.d/system-auth. This file is included in most of the other files in pam.d, so changes here propagate nicely. Updates to pambase may change this file.

Make pam_ldap.so sufficient at the top of each section, except in the session section, where we make it optional.

/etc/pam.d/system-auth

auth      sufficient pam_ldap.so
auth      required  pam_unix.so     try_first_pass nullok
auth      optional  pam_permit.so
auth      required  pam_env.so

account   sufficient pam_ldap.so
account   required  pam_unix.so
account   optional  pam_permit.so
account   required  pam_time.so

password  sufficient pam_ldap.so
password  required  pam_unix.so     try_first_pass nullok sha512 shadow
password  optional  pam_permit.so

session   required  pam_limits.so
session   required  pam_unix.so
session   optional  pam_ldap.so
session   optional  pam_permit.so

Then edit both /etc/pam.d/su and /etc/pam.d/su-l identically. The su-l file is used when the user runs su --login.

Make pam_ldap.so sufficient at the top of each section, and add use_first_pass to pam_unix in the auth section.

/etc/pam.d/su

#%PAM-1.0
auth      sufficient    pam_ldap.so
auth      sufficient    pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
#auth     sufficient    pam_wheel.so trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
#auth     required      pam_wheel.so use_uid
auth      required	pam_unix.so use_first_pass
account   sufficient    pam_ldap.so
account   required	pam_unix.so
session   sufficient    pam_ldap.so
session   required	pam_unix.so

To enable users to edit their password, edit /etc/pam.d/passwd:

/etc/pam.d/passwd

#%PAM-1.0
password        sufficient      pam_ldap.so
#password       required        pam_cracklib.so difok=2 minlen=8 dcredit=2 ocredit=2 retry=3
#password       required        pam_unix.so sha512 shadow use_authtok
password        required        pam_unix.so sha512 shadow nullok

Create home folders at login

If you want home folders to be created at login (eg: if you aren't using NFS to store home folders), edit /etc/pam.d/system-login and add pam_mkhomedir.so to the session section above any "sufficient" items. This will cause home folder creation when logging in at a tty, from ssh, xdm, kdm, gdm, etc. You might choose to edit additional files in the same way, such as /etc/pam.d/su and /etc/pam.d/su-l to enable it for su and su --login. If you don't want to do this for ssh logins, edit system-local-login instead of system-login, etc.

/etc/pam.d/system-login

...top of file not shown...
session    optional   pam_loginuid.so
session    include    system-auth
session    optional   pam_motd.so          motd=/etc/motd
session    optional   pam_mail.so          dir=/var/spool/mail standard quiet
-session   optional   pam_systemd.so
session    required   pam_env.so
session    required   pam_mkhomedir.so skel=/etc/skel umask=0022

/etc/pam.d/su-l

...top of file not shown...
session         required        pam_mkhomedir.so skel=/etc/skel umask=0022
session         sufficient      pam_ldap.so
session         required        pam_unix.so

Enable sudo

To enable sudo from an LDAP user, edit /etc/pam.d/sudo. You'll also need to modify sudoers accordingly.

/etc/pam.d/sudo

#%PAM-1.0
auth      sufficient    pam_ldap.so
auth      required      pam_unix.so  try_first_pass
auth      required      pam_nologin.so

Resources

The official page of the nss-pam-ldapd packet

The PAM and NSS page at the Debian Wiki 1 2

Using LDAP for single authentication

Heterogeneous Network Authentication Introduction

Discussion on suse's mailing lists about nss-pam-ldapd

@@ Line 1: / Line 1: @@
-[[Category:Networking]] [[Category:Security]]
+[[Category:Networking]]
+[[Category:Security]]
+{{Related articles start}}
+{{Related|OpenLDAP}}
+{{Related|LDAP Hosts}}
+{{Related articles end}}
 == Introduction and Concepts ==
 This is a guide on how to configure an Arch Linux installation to authenticate against an LDAP directory. This LDAP directory can be either local (installed on the same computer) or network (e.g. in a lab environment where central authentication is desired).
-The guide will be divided in two parts. The first part deals with how to setup an [[OpenLDAP]] server that hosts the authentication directory. The second part deals with how to setup the NSS and PAM modules that are required for the authentication scheme to work on the client computers. If you just want to configure Arch to authenticated against an already existing LDAP server then you can skip to the second part.
+The guide is divided into two parts. The first part deals with how to setup an [[OpenLDAP]] server that hosts the authentication directory. The second part deals with how to setup the NSS and PAM modules that are required for the authentication scheme to work on the client computers. If you just want to configure Arch to authenticate against an already existing LDAP server, you can skip to the second part.
 === NSS and PAM ===
@@ Line 18: / Line 24: @@
 You can read about installation and basic configuration in the [[OpenLDAP]] article. After you have completed that, return here.
+=== Set up access controls ===
+To make sure that no-one can read the (encrypted) passwords from the LDAP server, but a user can edit their own password, add the following to {{ic|/etc/openldap/slapd.conf}} and restart {{ic|slapd.service}} afterwards:
+{{hc|slapd.conf|2=
+access to attrs=userPassword
+        by self write
+        by anonymous auth
+        by * none
+access to *
+        by self write
+        by * read
+}}
 === Populate LDAP Tree with Base Data ===
-Create a file called {{ic|base.ldif}} with the following text:
+Create a temporarily file called {{ic|base.ldif}} with the following text.
+{{note|If you have a different domain name then alter "example" and "org" to your needs}}
 {{hc|base.ldif|<nowiki>
 # example.org
 dn: dc=example,dc=org
+dc: example
+o: Example Organization
 objectClass: dcObject
 objectClass: organization
-o: Example Organization
-dc: example
 # Manager, example.org
@@ Line 35: / Line 57: @@
 cn: Manager
 description: LDAP administrator
-roleOccupant: dc=example,dc=org
 objectClass: organizationalRole
 objectClass: top
+roleOccupant: dc=example,dc=org
 # People, example.org
@@ Line 45: / Line 67: @@
 objectClass: organizationalUnit
-# Group, example.org
+# Groups, example.org
-dn: ou=Group,dc=example,dc=org
+dn: ou=Groups,dc=example,dc=org
-ou: Group
+ou: Groups
 objectClass: top
 objectClass: organizationalUnit
@@ Line 62: / Line 84: @@
 === Adding users ===
 To manually add a user, create an {{ic|.ldif}} file like this:
-{{hc|example.ldif|<nowiki>
+{{hc|user_joe.ldif|<nowiki>
 dn: uid=johndoe,ou=People,dc=example,dc=org
 objectClass: top
@@ Line 87: / Line 109: @@
 </nowiki>}}
-the {{ic|xxxxxxxxxx}} in the {{ic|userPassword}} entry should be replaced with the value in {{ic|/etc/shadow}}.
+The {{ic|xxxxxxxxxx}} in the {{ic|userPassword}} entry should be replaced with the value in {{ic|/etc/shadow}} or use the {{ic|slappasswd}} command. Now add the user:
-You can automatically migrate all of your local accounts (and groups, etc.) to the LDAP directory using PADL Software's [http://www.padl.com/OSS/MigrationTools.html Migration Tools].
+ $ ldapadd -D "cn=Manager,dc=example,dc=org" -W -f user_joe.ldif
+{{Note|You can automatically migrate all of your local accounts (and groups, etc.) to the LDAP directory using PADL Software's [http://www.padl.com/OSS/MigrationTools.html Migration Tools].}}
 == Client Setup ==
@@ Line 108: / Line 132: @@
 Edit {{ic|/etc/nslcd.conf}} and change the {{ic|base}} and {{ic|uri}} lines to fit your ldap server setup.
-Restart {{ic|nslcd.service}}.
+Start {{ic|nslcd.service}} using systemd.
 You now should see your LDAP users when running {{ic|getent passwd}} on the client.
@@ Line 124: / Line 148: @@
 {{Tip|If you want to prevent UID clashes with local users on your system, you might want to include {{ic|minimum_uid&#61;10000}} or similar on the end of the {{ic|pam_ldap.so}} lines. You'll have to make sure the LDAP server returns uidNumber fields that match the restriction.}}
-{{Note|Each facility (auth, session, password, account) forms a separate chain and the order matters. Rule of thumb is ''sufficient'' lines before ''required'' lines and ''optional'' lines at the end. When adding your {{ic|pam_ldap.so}} lines, don't change the relative order of the other lines without good reason! Simply insert LDAP within the chain.}}
+{{Note|Each facility (auth, session, password, account) forms a separate chain and the order matters. Sufficient lines will sometimes "short circuit" and skip the rest of the section, so the rule of thumb for ''auth'', ''password'', and ''account'' is ''sufficient'' lines before ''required'', but after required lines for the ''session'' section; ''optional'' can almost always go at the end. When adding your {{ic|pam_ldap.so}} lines, don't change the relative order of the other lines without good reason! Simply insert LDAP within the chain.}}
 First edit {{ic|/etc/pam.d/system-auth}}. This file is included in most of the other files in {{ic|pam.d}}, so changes here propagate nicely. Updates to {{pkg|pambase}} may change this file.
@@ Line 168: / Line 192: @@
 }}
-To enable sudo from an LDAP user, edit {{ic|/etc/pam.d/sudo}}. You'll also need to modify sudoers accordingly.
+To enable users to edit their password, edit {{ic|/etc/pam.d/passwd}}:
-{{hc|/etc/pam.d/sudo|
+{{hc|/etc/pam.d/passwd|2=
 #%PAM-1.0
-'''auth      sufficient    pam_ldap.so'''
+'''password        sufficient      pam_ldap.so'''
-auth      required      pam_unix.so
+#password       required        pam_cracklib.so difok=2 minlen=8 dcredit=2 ocredit=2 retry=3
-auth      required      pam_nologin.so
+#password       required        pam_unix.so sha512 shadow use_authtok
+password        required        pam_unix.so sha512 shadow nullok
 }}
-If you want home folders to be created at login (eg: if you aren't using NFS to store home folders), edit {{ic|/etc/pam.d/system-login}} and {{ic|/etc/pam.d/su-l}} add pam_mkhomedir.so to the session section above any "sufficient" items. This will cause home folder creation when logging in at a tty, from ssh, xdm, kdm, gdm, etc and when using "su --login". You might choose to edit addition files, such as {{ic|/etc/pam.d/su}}, if you don't want ssh then system-local-login instead of system-login, etc.
+==== Create home folders at login ====
+If you want home folders to be created at login (eg: if you aren't using NFS to store home folders), edit {{ic|/etc/pam.d/system-login}} and add {{ic|pam_mkhomedir.so}} to the ''session'' section above any "sufficient" items. This will cause home folder creation when logging in at a tty, from ssh, xdm, kdm, gdm, etc. You might choose to edit additional files in the same way, such as {{ic|/etc/pam.d/su}} and {{ic|/etc/pam.d/su-l}} to enable it for {{ic|su}} and {{ic|su --login}}. If you don't want to do this for ssh logins, edit {{ic|system-local-login}} instead of {{ic|system-login}}, etc.
 {{hc|/etc/pam.d/system-login|
@@ Line 194: / Line 222: @@
 session         sufficient      pam_ldap.so
 session         required        pam_unix.so
+}}
+==== Enable sudo ====
+To enable sudo from an LDAP user, edit {{ic|/etc/pam.d/sudo}}. You'll also need to modify sudoers accordingly.
+{{hc|/etc/pam.d/sudo|
+#%PAM-1.0
+'''auth      sufficient    pam_ldap.so'''
+auth      required      pam_unix.so  '''try_first_pass'''
+auth      required      pam_nologin.so
 }}

Difference between revisions of "LDAP authentication"

Revision as of 22:09, 12 January 2014

Contents

Introduction and Concepts

NSS and PAM

LDAP Server Setup

Installation

Set up access controls

Populate LDAP Tree with Base Data

Adding users

Client Setup

NSS Configuration

Name Service Cache Daemon

PAM Configuration

Create home folders at login

Enable sudo

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