Configuring openldap

This article is a copy of Installing openldap just to make sure I have it always. I am skipping the installing stuff, that is straight forward.

Installing

Openldap is not available as an RPM package, therefor it is build from source. The downloading, untarring, bla bla bla, the ususal stuff. The most important thing, the version number, mine is 2.4.48 and the configure line:

./configure --enable-debug --enable-dynamic --enable-syslog --enable-proctitle --enable-ipv6 --enable-local --enable-slapd --enable-dynacl --enable-aci --enable-cleartext --enable-crypt --enable-lmpasswd --enable-spasswd --enable-modules --enable-rewrite --enable-rlookups --enable-slapi --disable-slp --enable-backends=mod --enable-bdb=yes --enable-hdb=yes --enable-mdb=yes --enable-monitor=yes --disable-ndb --enable-overlays=mod --disable-static --enable-shared --enable-moznss-compatibility=yes --with-cyrus-sasl --without-fetch --with-threads --with-pic --with-gnu-ld --libexecdir=/usr/lib64 --disable-sql --prefix=/usr --sysconfdir=/etc

Then the usual,

make depend
make -j 17
make install

The latter will fail, but it shows you if the paths are ok.

sudo make install

Add users and directories

Create the user:

sudo useradd -r -M -d /var/lib/openldap -u 55 -s /usr/sbin/nologin ldap

and create the tmp map during boot in ‘/usr/lib/tmpfiles.d/openldap.conf’:

d /var/run/openldap 0750 ldap ldap

This was not mentioned anywhere!

Create OpenLDAP data and database directories

mkdir /var/lib/openldap /etc/openldap/slapd.d

Set the proper ownership and permissions on OpenLDAP directories and configuration files.

chown -R ldap:ldap /var/lib/openldap
chown root:ldap /etc/openldap/slapd.conf
chmod 640 /etc/openldap/slapd.conf

Create OpenLDAP Systemd Service

In order to run OpenLDAP as a service, you need to create a systemd service file as shown below.

vim /etc/systemd/system/slapd.service

[Unit]
Description=OpenLDAP Server Daemon
After=syslog.target network-online.target
Documentation=man:slapd
Documentation=man:slapd-mdb

[Service]
Type=forking
PIDFile=/var/lib/openldap/slapd.pid
Environment="SLAPD_URLS=ldap:/// ldapi:/// ldaps:///"
Environment="SLAPD_OPTIONS=-F /etc/openldap/slapd.d"
ExecStart=/usr/libexec/slapd -u ldap -g ldap -h ${SLAPD_URLS} $SLAPD_OPTIONS

[Install]
WantedBy=multi-user.target

Save and quit the service file. Do not run the service yet.

Create OpenLDAP SUDO Schema

To configure LDAP with support sudo, first, check if your version of installed sudo supports LDAP.

sudo -V |  grep -i "ldap"

If sudo supports LDAP, you should see the lines below;

...
ldap.conf path: /etc/sudo-ldap.conf
ldap.secret path: /etc/ldap.secret

Check if LDAP sudo schema is available.

rpm -ql sudo |  grep -i schema.openldap
/usr/share/doc/sudo/schema.OpenLDAP

Copy the schema.OpenLDAP to the schema directory.

cp /usr/share/doc/sudo/schema.OpenLDAP  /etc/openldap/schema/sudo.schema

Next, you need to create sudo schema ldif file. Run the command below to create the sudo.ldif file. This ldif file is obtained from Lullabot github repository.

cat << 'EOL' > /etc/openldap/schema/sudo.ldif
dn: cn=sudo,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: sudo
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.1 NAME 'sudoUser' DESC 'User(s) who may  run sudo' EQUALITY caseExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.2 NAME 'sudoHost' DESC 'Host(s) who may run sudo' EQUALITY caseExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.3 NAME 'sudoCommand' DESC 'Command(s) to be executed by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.4 NAME 'sudoRunAs' DESC 'User(s) impersonated by sudo (deprecated)' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.5 NAME 'sudoOption' DESC 'Options(s) followed by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.6 NAME 'sudoRunAsUser' DESC 'User(s) impersonated by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.7 NAME 'sudoRunAsGroup' DESC 'Group(s) impersonated by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcObjectClasses: ( 1.3.6.1.4.1.15953.9.2.1 NAME 'sudoRole' SUP top STRUCTURAL DESC 'Sudoer Entries' MUST ( cn ) MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoRunAsUser $ sudoRunAsGroup $ sudoOption $ description ) )
EOL

Update SLAPD Database

Edit the SLAPD LDIF file, /etc/openldap/slapd.ldif, and update it as follows;

mv /etc/openldap/slapd.ldif /etc/openldap/slapd.ldif.bak
vi /etc/openldap/slapd.ldif
dn: cn=config
objectClass: olcGlobal
cn: config
olcArgsFile: /var/lib/openldap/slapd.args
olcPidFile: /var/lib/openldap/slapd.pid

dn: cn=schema,cn=config
objectClass: olcSchemaConfig
cn: schema

dn: cn=module,cn=config
objectClass: olcModuleList
cn: module
olcModulepath: /usr/libexec/openldap
olcModuleload: back_mdb.la

include: file:///etc/openldap/schema/core.ldif
include: file:///etc/openldap/schema/cosine.ldif
include: file:///etc/openldap/schema/nis.ldif
include: file:///etc/openldap/schema/inetorgperson.ldif
include: file:///etc/openldap/schema/samba.ldif
include: file:///etc/openldap/schema/ppolicy.ldif
include: file:///etc/openldap/schema/sudo.ldif

dn: olcDatabase=frontend,cn=config
objectClass: olcDatabaseConfig
objectClass: olcFrontendConfig
olcDatabase: frontend
olcAccess: to dn.base="cn=Subschema" by * read
olcAccess: to *
  by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by * none

dn: olcDatabase=config,cn=config
objectClass: olcDatabaseConfig
olcDatabase: config
olcRootDN: cn=config
olcAccess: to *
  by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by * none
  • To update the SLAPD database from the information provided on the SLAPD LDIF file above, use slapadd command with the option -n 0 which creates the first database.

  • To specify the configuration directory, /etc/openldap/slapd.d, use option -F and option -l to specify location of the LDIF file above.

Before you can write the changes to the database, perform a dry run to see what would happen. Pass -u option to slapadd command.

slapadd -n 0 -F /etc/openldap/slapd.d -l /etc/openldap/slapd.ldif -u

If the command above executes with no error, implement the changes.

slapadd -n 0 -F /etc/openldap/slapd.d -l /etc/openldap/slapd.ldif

This command creates slapd database configurations under /etc/openldap/slapd.d directory.

ls /etc/openldap/slapd.d
'cn=config'  'cn=config.ldif'

Set the user and group ownership of the /etc/openldap/slapd.d directory and the files in it to ldap user.

chown -R ldap:ldap /etc/openldap/slapd.d

Running SLAPD Service

Reload systemd configurations and start and enable OpenLDAP service to run on boot.

systemctl daemon-reload
systemctl enable --now slapd

Check the status;

systemctl status slapd
● slapd.service - OpenLDAP Server Daemon
   Loaded: loaded (/etc/systemd/system/slapd.service; enabled; vendor preset: disabled)
   Active: active (running) since Sat 2019-12-07 12:10:52 EST; 6s ago
     Docs: man:slapd
           man:slapd-mdb
   Process: 14975 ExecStart=/usr/libexec/slapd -u ldap -g ldap -h ${SLAPD_URLS} $SLAPD_OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 14976 (slapd)
    Tasks: 2 (limit: 5061)
   Memory: 3.0M
   CGroup: /system.slice/slapd.service
           └─14976 /usr/libexec/slapd -u ldap -g ldap -h ldap:/// ldapi:/// ldaps:/// -F /etc/openldap/slapd.d

Configure OpenLDAP Logging on CentOS 8

To enable OpenLDAP to log connections, operations, results statistics, create and ldif file and update the database as follows. Such OpenLDAP logging is enabled on log level 256 with keyword stats by modifying the olcLogLevel attribute as shown below.

vim enable-ldap-log.ldif
dn: cn=config
changeType: modify
replace: olcLogLevel
olcLogLevel: stats
ldapmodify -Y external -H ldapi:/// -f enable-ldap-log.ldif
ldapsearch -Y EXTERNAL -H ldapi:/// -b cn=config "(objectClass=olcGlobal)" olcLogLevel -LLL -Q
dn: cn=config
olcLogLevel: stats

Configure Rsyslog to enable OpenLDAP to log to a specific file. By default, OpenLDAP logs to local4 facility.

echo "local4.* /var/log/slapd.log" >> /etc/rsyslog.conf

Restart Rsyslog

systemctl restart rsyslog

You should now be able to read the LDAP logs on, /var/log/slapd.log.

Create OpenLDAP Default Root DN

Next, create MDB database defining the root DN as well as the access control lists.

First, generate the root DN password.

slappasswd
New password: ENTER PASSWORD
Re-enter new password: RE-ENTER PASSWORD
{SSHA}qAZah0xybYLcMfPUAN0SG4ki8JxC4bIF

Paste the password hash generated above as the value of olcRootPW in the Root DN ldif file below.

vim rootdn.ldif

Replace the domain components, dc=ldapmaster,dc=kifarunix-demo,dc=com with your appropriate names.

dn: olcDatabase=mdb,cn=config
objectClass: olcDatabaseConfig
objectClass: olcMdbConfig
olcDatabase: mdb
olcDbMaxSize: 42949672960
olcDbDirectory: /var/lib/openldap
olcSuffix: dc=ldapmaster,dc=kifarunix-demo,dc=com
olcRootDN: cn=admin,dc=ldapmaster,dc=kifarunix-demo,dc=com
olcRootPW: {SSHA}5Hcgjj4gtcr/exLcdSRuYgH6bFhIqkSe
olcDbIndex: uid pres,eq
olcDbIndex: cn,sn pres,eq,approx,sub
olcDbIndex: mail pres,eq,sub
olcDbIndex: objectClass pres,eq
olcDbIndex: loginShell pres,eq
olcDbIndex: sudoUser,sudoHost pres,eq
olcAccess: to attrs=userPassword,shadowLastChange,shadowExpire
  by self write
  by anonymous auth
  by dn.subtree="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by dn.subtree="ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com" read
  by * none
olcAccess: to dn.subtree="ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com" by dn.subtree="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by * none
olcAccess: to dn.subtree="dc=ldapmaster,dc=kifarunix-demo,dc=com" by dn.subtree="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by users read
  by * none

Read more about ACL on OpenLDAP Access Control.

Updated the slapd database with the content above;

ldapadd -Y EXTERNAL -H ldapi:/// -f rootdn.ldif

Configure OpenLDAP with SSL/TLS

To secure OpenLDAP communication between the client and the server, configured it to use SSL/TLS certificates.

In this guide, we are self-signed certificates. You can choose to obtain the commercially signed and trusted certificates from your preferred CAs, for production environments.

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/pki/tls/ldapserver.key -out /etc/pki/tls/ldapserver.crt
chown ldap:ldap /etc/pki/tls/{ldapserver.crt,ldapserver.key}

Update the OpenLDAP Server TLS certificates attributes.

vi add-tls.ldif
dn: cn=config
changetype: modify
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/pki/tls/ldapserver.crt
-
add: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/pki/tls/ldapserver.key
-
add: olcTLSCertificateFile
olcTLSCertificateFile: /etc/pki/tls/ldapserver.crt

Note that we have used self-signed certificate as both the certificate and the CA certificate.

ldapadd -Y EXTERNAL -H ldapi:/// -f add-tls.ldif

You can confirm this by running;

slapcat -b "cn=config" | grep olcTLS
olcTLSCACertificateFile: /etc/pki/tls/ldapserver.crt
olcTLSCertificateKeyFile: /etc/pki/tls/ldapserver.key
olcTLSCertificateFile: /etc/pki/tls/ldapserver.crt

Change the location of the CA certificate on /etc/openldap/ldap.conf.

vim /etc/openldap/ldap.conf
...
#TLS_CACERT     /etc/pki/tls/cert.pem
TLS_CACERT     /etc/pki/tls/ldapserver.crt

Create OpenLDAP Base DN

Next, create your base DN or search base to define your organization structure and directory.

vim basedn.ldif

Replace the domain components and organization units accordingly.

dn: dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: dcObject
objectClass: organization
objectClass: top
o: Kifarunix-demo
dc: ldapmaster

dn: ou=groups,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalUnit
objectClass: top
ou: groups

dn: ou=people,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalUnit
objectClass: top
ou: people
ldapadd -Y EXTERNAL -H ldapi:/// -f basedn.ldif

Create OpenLDAP User Accounts

You can add users to your OpenLDAP server. Create an ldif file to define your users as follows.

vim users.ldif
dn: uid=johndoe,ou=people,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
uid: johndoe
cn: John
sn: Doe
loginShell: /bin/bash
uidNumber: 10000
gidNumber: 10000
homeDirectory: /home/johndoe
shadowMax: 60
shadowMin: 1
shadowWarning: 7
shadowInactive: 7
shadowLastChange: 0

dn: cn=johndoe,ou=groups,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: posixGroup
cn: johndoe
gidNumber: 10000
memberUid: johndoe

Add the user to the OpenLDAP database.

ldapadd -Y EXTERNAL -H ldapi:/// -f users.ldif

Setting password for LDAP User

To set the password for user above, run the command below;

ldappasswd -H ldapi:/// -Y EXTERNAL -S "uid=johndoe,ou=people,dc=ldapmaster,dc=kifarunix-demo,dc=com"

Create OpenLDAP Bind DN and Bind DN User

Bind DN user is used for performing LDAP operations such as resolving User IDs and group IDs. In this guide, we create a bind DN ou called system. Note the access controls associated with this ou as defined on the root DN above.

List the Access control lists on the database;

ldapsearch -Q -LLL -Y EXTERNAL -H ldapi:/// -b cn=config '(olcDatabase={1}mdb)' olcAccess

Create the BindDN user password.

slappasswd
New password: Password
Re-enter new password: Password
{SSHA}Z7qPE2f8oRfHMo1DSbzdOqbr4jNgqBpC

Paste the password hash value above as the value of userPassword attribute in the file below;

vim bindDNuser.ldif

dn: ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalUnit
objectClass: top
ou: system

dn: cn=readonly,ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalRole
objectClass: simpleSecurityObject
cn: readonly
userPassword: {SSHA}Z7qPE2f8oRfHMo1DSbzdOqbr4jNgqBpC
description: Bind DN user for LDAP Operations
ldapadd -Y EXTERNAL -H ldapi:/// -f bindDNuser.ldif

Allow OpenLDAP Service on Firewall

To allow remote clients to query OpenLDAP server, allow the ldap (389 UDP/TCP) and ldaps (636 UDP/TCP) service on firewall.

firewall-cmd --add-service={ldap,ldaps} --permanent

firewall-cmd --reload

Testing OpenLDAP Authentication

Well, there you go. You have learnt how to install and setup OpenLDAP server on CentOS 8. To verify that users can actually connect to the systems via the OpenLDAP server, you need to configure OpenLDAP clients on the remote systems.