Install OpenLDAP Authentication Server on CentOS 7

OpenLDAP is a free and open-source implementation of the Light Directory Access Protocol (LDAP). The LDAP is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an IP network. Directory services play an important role in developing intranet and Internet applications by allowing the sharing of information about users, systems, networks, services, and applications throughout the network.

In this post, I will demonstrate you how to configure a Central Remote Authentication Server using OpenLDAP v2.4 on platform CentOS / RHEL 7.

 

Table of Contents:

• System Specification
• Configure LDAP Server on CentOS 7
• Configure LDAP Client on CentOS 7

System Specification:

For this demonstration, I have provisioned a VM with following specification. Please do not confuse these specification with the minimum system requirements for OpenLDAP.

• CPU - 2.4 Ghz (1 core)
• Memory - 1 GB
• Storage - 20 GB
• Swap - 2 GB
• Operating System - CentOS 7.0

I have done some initial configurations in VM, that includes setting up hostname, IP address and Yum Repository.

• Hostname - ldapserver.itlab.com
• IP Address - 192.168.116.3/24

 

Configure LDAP Server on CentOS 7:

Login to VM with root user, and install openldap packages.

# yum -y install openldap compat-openldap openldap-clients openldap-servers openldap-devel

Create database from template.

# cp /usr/share/openldap-servers/DB_CONFIG.example /var/lib/ldap/DB_CONFIG
# slaptest -u
config file testing succeeded
# chown ldap:ldap /var/lib/ldap/*

Start and Enable the slapd service.

# systemctl enable slapd && systemctl start slapd
ln -s '/usr/lib/systemd/system/slapd.service' '/etc/systemd/system/multi-user.target.wants/slapd.service'

Allow ldaps port in Firewall.

# firewall-cmd --permanent --add-service=ldaps
success
# firewall-cmd --reload
success

Configure OpenLDAP syslog.

# cat >> /etc/rsyslog.conf << EOF
> #LDAP Logging
> local4.* /var/log/openldap.log
> EOF
# systemctl restart rsyslog

Add required schemas to our OpenLDAP Directory.

# ldapadd -Y EXTERNAL -H ldapi:/// -D "cn=config" -f /etc/openldap/schema/cosine.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
adding new entry "cn=cosine,cn=schema,cn=config"

# ldapadd -Y EXTERNAL -H ldapi:/// -D "cn=config" -f /etc/openldap/schema/nis.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
adding new entry "cn=nis,cn=schema,cn=config"

Generate Password hash 123 for Directory Manager.

# slappasswd
New password:
Re-enter new password:
{SSHA}mNOljCtwWbG0P88Hu+jqsrkUOzjfqvak

Copy the Password hash, we will need it in later configurations. Add initial database configurations.

# mkdir ~/ldap
# cd ~/ldap

# cat > db.ldif << EOF
> dn: olcDatabase={2}hdb,cn=config
> changetype: modify
> replace: olcSuffix
> olcSuffix: dc=itlab,dc=com
>
> dn: olcDatabase={2}hdb,cn=config
> changetype: modify
> replace: olcRootDN
> olcRootDN: cn=ldapadm,dc=itlab,dc=com
>
> dn: olcDatabase={2}hdb,cn=config
> changetype: modify
> replace: olcRootPW
> olcRootPW: {SSHA}mNOljCtwWbG0P88Hu+jqsrkUOzjfqvak
> EOF

# ldapmodify -Y EXTERNAL  -H ldapi:/// -f db.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
modifying entry "olcDatabase={2}hdb,cn=config"

modifying entry "olcDatabase={2}hdb,cn=config"

modifying entry "olcDatabase={2}hdb,cn=config"

Since, we are planning to run this service in TLS mode, therefore, must required to create security certificates for this purpose. For simplicity, I am using Self-Signed certificates, However, you can use a Signed Certificate, if you have a Certification Authority (CA) configured for your network.

# openssl req -new -x509 -nodes -out /etc/openldap/certs/ldapserver.pem -keyout /etc/openldap/certs/ldapserver.key -days 365
Generating a 2048 bit RSA private key
.........................+++
..................................................................+++
writing new private key to '/etc/openldap/certs/ldapserver.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:PK
State or Province Name (full name) []:Sindh
Locality Name (eg, city) [Default City]:Karachi
Organization Name (eg, company) [Default Company Ltd]:XYZ
Organizational Unit Name (eg, section) []:IT Lab
Common Name (eg, your name or your server's hostname) []:ldapserver.itlab.com
Email Address []:root@ldapserver.itlab.com

# cd /etc/openldap/certs
# chown ldap:ldap *
# chmod 600 ldapserver.key

Edit the following directive in /etc/sysconfig/slapd to enable service to run in TLS mode.

SLAPD_URLS="ldapi:/// ldap:/// ldaps:///"

Now, add security certificate and private key to LDAP configurations.

# cd ~/ldap
# cat > cert.ldif << EOF
> dn: cn=config
> changetype: modify
> replace: olcTLSCertificateFile
> olcTLSCertificateFile: /etc/openldap/certs/ldapserver.pem
>
> dn: cn=config
> changetype: modify
> replace: olcTLSCertificateKeyFile
> olcTLSCertificateKeyFile: /etc/openldap/certs/ldapserver.key
>
> dn: cn=config
> changetype: modify
> replace: olcLogLevel
> olcLogLevel: -1
> EOF

# ldapmodify -Y EXTERNAL  -H ldapi:/// -f cert.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
modifying entry "cn=config"

modifying entry "cn=config"

modifying entry "cn=config"

Create directory, LDAP Manager user, and two Organisational units for holding users and groups entries.

# cd ~/ldap
# cat > base.ldif << EOF
> dn: dc=itlab,dc=com
> dc: itlab
> objectClass: top
> objectClass: domain
>
> dn: cn=ldapadm ,dc=itlab,dc=com
> objectClass: organizationalRole
> cn: ldapadm
> description: LDAP Manager
>
> dn: ou=People,dc=itlab,dc=com
> objectClass: organizationalUnit
> ou: People
>
> dn: ou=Groups,dc=itlab,dc=com
> objectClass: organizationalUnit
> ou: Groups
> EOF

# ldapadd -x -W -D "cn=ldapadm,dc=itlab,dc=com" -f base.ldif
Enter LDAP Password:
adding new entry "dc=itlab,dc=com"

adding new entry "cn=ldapadm ,dc=itlab,dc=com"

adding new entry "ou=People,dc=itlab,dc=com"

adding new entry "ou=Groups,dc=itlab,dc=com"

Define access levels for the directory.

# cd ~/ldap
# cat > access.ldif << EOF
> dn: olcDatabase={1}monitor,cn=config
> changetype: modify
> replace: olcAccess
> olcAccess: {0}to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external, cn=auth" read by dn.base="cn=ldapadm,dc=itlab,dc=com" read by * none
>
> changetype: modify
> replace: olcAccess
> olcAccess: {0}to dn.subtree="dc=itlab,dc=com" by dn.base="cn=ldapadm,dc=itlab,dc=com" manage by * read
> EOF

# ldapmodify -Y EXTERNAL  -H ldapi:/// -f access.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
modifying entry "olcDatabase={1}monitor,cn=config"

Let’s create three groups. Groups ahmer & mansoor here are defined to be utilized as the Primary groups for the Users ahmer & mansoor. While group dba will be used as a suplementary group for both users.

# cd ~/ldap
# cat > groups.ldif << EOF
> dn: cn=ahmer,ou=Groups,dc=itlab,dc=com
> cn: ahmer
> objectClass: posixGroup
> objectClass: top
> gidNumber: 10001
> memberuid: ahmer
>
> dn: cn=mansoor,ou=Groups,dc=itlab,dc=com
> cn: mansoor
> objectClass: posixGroup
> objectClass: top
> gidNumber: 10002
> memberuid: mansoor
>
> dn: cn=dba,ou=Groups,dc=itlab,dc=com
> cn: dba
> objectClass: posixGroup
> objectClass: top
> gidNumber: 10003
> memberuid: ahmer
> memberuid: mansoor
> EOF

# ldapadd -x -W -D "cn=ldapadm,dc=itlab,dc=com" -f groups.ldif
Enter LDAP Password:
adding new entry "cn=ahmer,ou=Groups,dc=itlab,dc=com"

adding new entry "cn=mansoor,ou=Groups,dc=itlab,dc=com"

adding new entry "cn=dba,ou=Groups,dc=itlab,dc=com"

Now create users.

# cd ~/ldap
# cat > users.ldif << EOF
> dn: uid=ahmer,ou=People,dc=itlab,dc=com
> uid: ahmer
> cn: ahmer
> objectClass: account
> objectClass: posixAccount
> objectClass: top
> objectClass: shadowAccount
> userPassword: {crypt}a
> shadowLastChange: 17665
> shadowMin: 0
> shadowMax: 99999
> shadowWarning: 7
> loginShell: /bin/bash
> uidNumber: 10001
> gidNumber: 10001
> homeDirectory: /home/ahmer
>
> dn: uid=mansoor,ou=People,dc=itlab,dc=com
> uid: mansoor
> cn: mansoor
> objectClass: account
> objectClass: posixAccount
> objectClass: top
> objectClass: shadowAccount
> userPassword: {crypt}a
> shadowLastChange: 17665
> shadowMin: 0
> shadowMax: 99999
> shadowWarning: 7
> loginShell: /bin/bash
> uidNumber: 10002
> gidNumber: 10002
> homeDirectory: /home/mansoor
> EOF

# ldapadd -x -W -D "cn=ldapadm,dc=itlab,dc=com" -f users.ldif
Enter LDAP Password:
adding new entry "uid=ahmer,ou=People,dc=itlab,dc=com"

adding new entry "uid=mansoor,ou=People,dc=itlab,dc=com"

Set passwords for the users.

# ldappasswd -S -x -D "cn=ldapadm,dc=itlab,dc=com" -W "uid=ahmer,ou=People,dc=itlab,dc=com"
New password:
Re-enter new password:
Enter LDAP Password:

# ldappasswd -S -x -D "cn=ldapadm,dc=itlab,dc=com" -W "uid=mansoor,ou=People,dc=itlab,dc=com"
New password:
Re-enter new password:
Enter LDAP Password:

We can also use an LDAP browser utility to manage our directory. Following is a screenshot of our directory at this time.

There are various commercial and free LDAP Directory Browsers and Admins tools are available. I used LDAPAdmin for this job.

 

Configure LDAP Client on CentOS 7:

Now, I am going to configure a Linux client to use our LDAP directory for Remote Authentication. I have a client machine here with hostname=Desktop1, that I use for this purpose. First of all, make sure that hostname of our LDAP Directory Server must be resolvable, because we are using Hostname ldapserver.itlab.com for the Common Name in the Security Certificate.

# echo 192.168.116.3 ldapserver.itlab.com ldapserver >> /etc/hosts

Now install required packages.

# yum -y install openldap sssd
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Repodata is over 2 weeks old. Install yum-cron? Or run: yum makecache fast
localyum                                                                                           | 4.1 kB  00:00:00
Package openldap-2.4.39-3.el7.x86_64 already installed and latest version
Package sssd-1.11.2-65.el7.x86_64 already installed and latest version
Nothing to do

# systemctl start sssd && systemctl enable sssd
ln -s '/usr/lib/systemd/system/sssd.service' '/etc/systemd/system/multi-user.target.wants/sssd.service'

Since, we are using LDAPS, therefore, we have to copy the Self-Signed Certificate to our client machine.

# scp root@ldapserver.itlab.com:/etc/openldap/certs/ldapserver.pem /etc/openldap/cacerts/ldapserver.pem
The authenticity of host 'ldapserver.itlab.com (192.168.116.3)' can't be established.
ECDSA key fingerprint is 4c:7f:83:39:d1:bc:ef:4c:fd:58:82:7b:36:ff:9e:f2.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'ldapserver.itlab.com,192.168.116.3' (ECDSA) to the list of known hosts.
root@ldapserver.itlab.com's password:
ldapserver.pem                                                                          100% 1452     1.4KB/s   00:00

Now configure Remote Authentication with LDAP on client machine.

# authconfig --update --enableldap --enableldapauth --enableldaptls --ldapserver=ldaps://ldapserver.itlab.com --ldapbasedn="dc=itlab,dc=com" --enablemkhomedir

Now connect using an LDAP User.

# su - ahmer
Creating directory '/home/ahmer'.
Last login: Mon May 28 11:28:17 PDT 2018 on pts/0
$ id
uid=10001(ahmer) gid=10001(ahmer) groups=10001(ahmer),10003(dba) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

Our client machine is now configured to authenticate to the OpenLDAP remote authentication server.