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Ashkan
Ashkan

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Time-based one-time passwords (TOTP) with OpenLDAP

#totp #ldap #2fa #openldap

Two-factor authentication (2FA) is a method of enhancing the security of online accounts by requiring two types of credentials: something you know, such as a password, and something you have, such as a device. One common way of implementing the second factor is using time-based one-time passwords (TOTP), which are unique numeric codes that are generated based on the current time and a shared secret key. TOTP codes are usually displayed by an authentication app on your smartphone or tablet, and they expire after a short period of time. TOTP is an open standard that is defined in RFC 6238 and supported by many applications and services.

In this article, we will install and configure OpenLDAP on Ubuntu 22.04 and implement TOTP. To implement OTP we need OpenLDAP 2.5 or higher.

NOTICE: This guide is for educational purposes only and is NOT meant to be used in production environments.

Install and configure OpenLDAP

Run the following command:

sudo apt install slapd ldap-utils
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Enter a new password:

Admin password prompt

To reconfigure the default configuration, run:

sudo dpkg-reconfigure slapd
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You will be asked to omit OpenLDAP configuration, select No.

Initial configuration

Enter your domain name:

Domain name

Enter your organization name:

Organization name

Provide the administration password and then confirm it:

Admin password

For this guide, when you get prompted to remove the database when slapd is purged, select Yes:

Purge database

And finally select Yes:

Move old database

Open ldap.conf with a text editor:

sudo vim /etc/ldap/ldap.conf
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Find and uncomment the following lines:

#BASE   dc=example,dc=com
#URI    ldap://ldap.example.com ldap://ldap-provider.example.com:666
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Edit these entries, replace BASE with your domain name, and URI with the URI to your ldap server:

BASE    dc=mydomain,dc=com
URI     ldap://ldap.mydomain.com
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Save the changes and exit the editor. You might need to edit the hosts file and provide the FQDN to your LDAP server and its IP address:

sudo vim /etc/hosts
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192.168.1.1 ldap.mydomain.com
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Creating user accounts

Create a file:

vim users-ou.ldif
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Enter the following contents:

dn: ou=people,dc=mydomain,dc=com
objectClass: organizationalUnit
objectClass: top
ou: people

dn: ou=groups,dc=mydomain,dc=com
objectClass: organizationalUnit
objectClass: top
ou: groups
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Save and close the file. Now run the following command:

ldapadd -x -D cn=admin,dc=mydomain,dc=com -W -f users-ou.ldif
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And enter your administration password. You should see an output like this:

Addin OU

You can use the following command to verify:

ldapsearch -Q -LLL -Y EXTERNAL -H ldapi://
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That should print something like this:

ldapsearch ou

Now create a password using the slappasswd command. Run the command and enter a password, then confirm it. You should get something like this:

slappasswd

Copy the hash. Now create another file:

vim user.ldif
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Enter the following contents:

dn: uid=johndoe,ou=people,dc=mydomain,dc=com
objectClass: inetOrgPerson
objectClass: organizationalPerson
objectClass: person
objectClass: posixAccount
objectClass: shadowAccount
objectClass: top
homeDirectory: /home/john
givenName: John
sn: Doe
cn: John Doe
uid: johndoe
displayName: John Doe
uidNumber: 8000
gidNumber: 8000
userPassword: {SSHA}eLp4NBSK1SV3VOFY3iUxI8P73vmOW/Lh
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Replace {SSHA}eLp4NBSK1SV3VOFY3iUxI8P73vmOW/Lh with hash you copied earlier. Run the following command to create a user account:

ldapadd -x -D cn=admin,dc=mydomain,dc=com -W -f user.ldif
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Create another file:

vim group.ldif
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Enter the contents below:

dn: cn=appusers,ou=groups,dc=mydomain,dc=com
objectClass: posixGroup
objectClass: top
cn: appusers
gidNumber: 10000
memberUid: uid=johndoe,ou=people,dc=mydomain,dc=com
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Apply the changes to create a group:

ldapadd -x -D cn=admin,dc=mydomain,dc=com -W -f group.ldif
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You can use ldapsearch -Q -LLL -Y EXTERNAL -H ldapi:// to verify the changes or use graphical tools such as the Apache Directory Studio to verify changes and manage your LDAP server.

Apache Directory Studio

Configure TOTP

First otp module must be loaded. Create a file:

vim otpload.ldif
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Enter the following contents:

dn: cn=module{0},cn=config
changetype: modify
add: olcModuleLoad
olcModuleLoad: otp.la
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Apply the changes:

sudo ldapmodify -Y EXTERNAL -H ldapi:// -D cn=config -W -f otpload.ldif
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The output should be like this:

otp load

Now the otp overlay must be added to databases. Create another file:

vim overlay.ldif
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Enter the following contents:

dn: olcOverlay=otp,olcDatabase={1}mdb,cn=config
objectClass: olcOverlayConfig
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Run the following command:

sudo ldapadd -Y EXTERNAL -H ldapi:// -D cn=config -W  -f overlay.ldif
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To set the otp parameters, create a file:

vim totp.ldif
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And enter the following contents:

dn: ou=people,dc=mydomain,dc=com
changetype: modify
add: objectClass
objectClass: oathTOTPParams
-
add: oathOTPLength
oathOTPLength: 6
-
add: oathHMACAlgorithm
oathHMACAlgorithm: 1.2.840.113549.2.7
-
add: oathTOTPTimeStepPeriod
oathTOTPTimeStepPeriod: 30
-
add: oathTOTPTimeStepWindow
oathTOTPTimeStepWindow: 3
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Run the command below to apply the configuration:

ldapmodify -x -D cn=admin,dc=mydomain,dc=com -W -f totp.ldif
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To be able to use TOTP, users need a key. This key is shared between the server and the user. The following command can be used to generate the key:

openssl rand 80 > key
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To use the key, create a file:

vim token.ldif
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Enter the contents like below:

dn: uid=johndoe,ou=people,dc=mydomain,dc=com
changetype: modify
add: objectClass
objectClass: oathTOTPToken
-
add: oathTOTPParams
oathTOTPParams: ou=people,dc=mydomain,dc=com
-
add: oathSecret
oathSecret:< file:key
-
add: objectClass
objectClass: oathTOTPUser
-
add: oathTOTPToken
oathTOTPToken: uid=johndoe,ou=people,dc=mydomain,dc=com
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The following command applies the changes:

ldapmodify -x -D cn=admin,dc=mydomain,dc=com -W -f token.ldif
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You can use qrencode to generate the QR code. First install it with the following command:

sudo apt install qrencode
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Use the commands below to generate the QR code:

base32 key > bkey
echo -n "otpauth://totp/myorg:johhdoe@mydomain.com?secret=$(<bkey)&issuer=myorg&period=30&digits=6&algorithm=SHA1" | qrencode -t ansiutf8
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QR

Now you can scan the QR code with an authenticator app such as the Google Authenticator.

How to authenticate?

Whenever you get asked to provide your password, enter your password followed by the code you get from the authenticator app. For example if your password is abcdef and the code that you get from the app is 123456, enter abcdef123456 as your password.

References and Further Reading

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