Difference between revisions of "OpenLDAP Authentication"

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[[Category:Networking]] [[Category:Security]]
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#REDIRECT [[LDAP Authentication]]
{{Merge|LDAP Authentication}}
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== Introduction and Concepts ==
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This is a guide on how to configure an Archlinux installation to authenticate against an OpenLDAP server.The openldap backend can be either local (installed on the same computer) or network (i.e in a lab environment where central authentication is desired).
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The guide will be divided in two parts. The first part deals with how to setup OpenLDAP locally and the second with how to setup the NSS and PAM modules required for the authentication scheme to work. If you just want to configure Arch to authenticated against an already excisting LDAP server then you can skip to the second part.
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=== OpenLDAP ===
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OpenLDAP is an open-source server implementation of the LDAP protocol. It is mainly used as an authentication backend to various services (the most famous one being Samba, which is used to emulate a domain controller) and basically holds the user data.
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The closest analogue to real life, would be the telephone directory. Another generalised explanation of what an LDAP server does is that it is a database (which it basically is, but it is not relational) which is optimised for accessing the data and not reading them.
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Commands relate to OpenLDAP that begin with ldap (like ldapsearch) are client-side utilities while commands that begin with slap (like slapcat) are server-side. Arch packages both in the {{pkg|openldap}} package, so you need to install it regardless of o local or network OpenLDAP install.
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=== NSS and PAM ===
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NSS (which stands for Name Service Switch) is a system mechanism to configure different sources for common configuration databases. For example, {{ic|/etc/passwd}} is a {{ic|file}} type source for the passwd database.
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PAM (which stands for Pluggable Authentication Module) is a machanism Linux (and most *nixes) uses to extend it's authentication schemes based on different plugins.
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So to summarize, we need to configure NSS to use the OpenLDAP server as a source for the {{ic|passwd}} {{ic|shadow}} and other configuration databases and then configure PAM to use these sources to authenticate it's users.
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== OpenLDAP Setup ==
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=== Installation ===
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You can read about installation and basic configuration in the [[OpenLDAP]] article. After you have completed that, return here.
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=== Populate LDAP Tree with Base Data ===
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Create a file called base.ldif with the following text:
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# example.org
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dn: dc=example,dc=org
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objectClass: dcObject
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objectClass: organization
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o: Example Organization
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dc: example
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# Manager, example.org
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dn: cn=Manager,dc=example,dc=org
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cn: Manager
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description: LDAP administrator
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roleOccupant: dc=example,dc=org
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objectClass: organizationalRole
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objectClass: top
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# People, example.org
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dn: ou=People,dc=example,dc=org
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ou: People
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objectClass: top
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objectClass: organizationalUnit
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# Group, example.org
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dn: ou=Group,dc=example,dc=org
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ou: Group
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objectClass: top
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objectClass: organizationalUnit
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Add it to your OpenLDAP Tree:
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ldapadd -x -D "cn=Manager,dc=example,dc=org" -W -f base.ldif
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Test to make sure the data was imported:
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ldapsearch -x -b 'dc=example,dc=org' '(objectclass=*)'
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== Client Setup ==
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[[pacman|Install]] {{Pkg|openldap}} from the [[official repositories]]. This is needed regardless of whether you run openldap on your machine or over the network.
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Next, [[pacman|install]] {{AUR|nss-pam-ldapd}} from the [[Arch User Repository]].
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There is the {{pkg|nss_ldap}} and {{pkg|pam_ldap}} from the [[Official Repositories|official repositories]]
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=== OpenLDAP ===
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Before you begin setting up PAM and NSS for ldap authentication, you should try to check if the LDAP server is available. You can do this easily with ldapsearch.
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You can search an LDAP server with the following command:
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{{bc|ldapsearch -x -H <URL> -b <BASE>}}
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{{Tip| {{ic|-x}} is required in all client commands because SASL authentication probably hasn't been configured.}}
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You can add the URL and BASE settings to {{ic|/etc/openldap/ldap.conf}} in order to avoid writing the everytime. All client-side ldap utilities use this file to read some general variables.
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{{Warning| If you created a self-signed certificate above you need to also add the following line or you will not be able connect to the server:
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{{ic|TLS_REQCERT allow}} }}
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=== NSS Configuration ===
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NSS is a system facility which manages different sources as configuration databases. For example {{ic|/etc/passwd}} is i {{ic|file}}-type source for the {{ic|passwd}} which by default stores the user accounts. nss_ldap is a plugin which allow NSS to see an OpenLDAP server as a source for these databases.
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Edit {{ic|/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 {{ic|ldap}} directive to the {{ic|passwd}}, {{ic|group}} and {{ic|shadow}} databases, so be sure your file looks like this:
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passwd: files ldap
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group: files ldap
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shadow: files ldap
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==== Name Service Cache Daemon ====
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NSCD is a daemon that NSS runs that is responsible for caching lookups and queries for network backends.
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{{Important| It is recommended to stop the daemon when troubleshooting because it may mask problems by serving cached queries}}
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READ THIS FIRST: [[https://bbs.archlinux.org/viewtopic.php?id=9401 NSCD Bugged in Arch Linux]]
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Fix nscd:
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mkdir -p /var/db/nscd/
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mkdir -p /var/run/nscd/
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Run nscd:
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{{bc|systemctl start nscd}}
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==== NSLCD ====
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=== PAM Configuration ===
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Edit {{ic|/etc/pam.d/login}}:
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auth            requisite      pam_securetty.so
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auth            requisite      pam_nologin.so
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auth            sufficient      pam_ldap.so             
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auth            required        pam_env.so
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auth            required        pam_unix.so nullok try_first_pass
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account        sufficient      pam_ldap.so
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account        required        pam_access.so
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account        required        pam_unix.so
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session        required        pam_motd.so
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session        required        pam_limits.so
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session        optional        pam_mail.so dir=/var/spool/mail standard
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session        optional        pam_lastlog.so
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session        required        pam_unix.so
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Edit {{ic|/etc/pam.d/passwd}}:
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password        sufficient      pam_ldap.so
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password        required        pam_unix.so shadow md5 nullok
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Edit {{ic|/etc/pam.d/shadow}}:
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auth            sufficient      pam_ldap.so
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auth            sufficient      pam_rootok.so
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auth            required        pam_unix.so
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account        sufficient      pam_ldap.so
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account        required        pam_unix.so
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session        sufficient      pam_ldap.so
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session        required        pam_unix.so
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password        sufficient      pam_ldap.so
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password        required        pam_permit.so
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edit {{ic|/etc/pam.d/su}}:
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auth            sufficient      pam_ldap.so
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auth            sufficient      pam_rootok.so
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auth            required        pam_unix.so use_first_pass
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account        sufficient      pam_ldap.so
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account        required        pam_unix.so
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session        sufficient      pam_ldap.so
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session        required        pam_unix.so
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edit {{ic|/etc/pam.d/sshd}}:
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auth            sufficient      pam_ldap.so
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auth            required        pam_securetty.so        #Disable remote root
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auth            required        pam_unix.so try_first_pass
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auth            required        pam_nologin.so
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auth            required        pam_env.so
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account        sufficient      pam_ldap.so
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account        required        pam_unix.so
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account        required        pam_time.so
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password        sufficient      pam_ldap.so
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password        required        pam_unix.so
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session        required        pam_unix_session.so
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session        required        pam_limits.so
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edit {{ic|/etc/pam.d/other}}:
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auth            sufficient      pam_ldap.so
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auth            required        pam_unix.so
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account        sufficient      pam_ldap.so
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account        required        pam_unix.so
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password        sufficient      pam_ldap.so
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password        required        pam_unix.so
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session        required        pam_unix.so
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== Resources ==
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[http://arthurdejong.org/nss-pam-ldapd/setup The official page of the nss-pam-ldapd packet]
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The PAM and NSS page at the Debian Wiki [http://wiki.debian.org/LDAP/NSS 1] [http://wiki.debian.org/LDAP/PAM 2]
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[http://www.fatofthelan.com/articles/articles.php?pid=24 Using LDAP for single authentication]
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[http://www.cs.dixie.edu/ldap/ Heterogeneous Network Authentication Introduction]
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[http://readlist.com/lists/suse.com/suse-linux-e/36/182642.html Discussion on suse's mailing lists about nss-pam-ldapd]
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Revision as of 00:59, 6 November 2013