fcenobi/openvpn

OpenVPN HA setup with Windows AD certs and authentication

OpenVPN

This document assumes OpenVPN Server is already installed and configured (minimum two) If not Follow the given link - https://help.ubuntu.com/lts/serverguide/openvpn.html

Step 1: Set Up CA in Windows AD

Follow the given doc - Setting Up a Certification Authority.docx	

Step 2: Create new Certificate template for VPN connection

Follow the given doc - Creating a new certificate template for User certificates.docx

Step 3: Configure User certificate Auto-Enrollment

Follow the given doc - Auto-Enrollment.docx

Step 4: Export CA certificate

Follow the given doc - Export CA Certificate.docx

Step 5: Export User certificate

Follow the given doc - Export AD cert _ key.docx

Step 6: Modify OpenVpn to use AD CA certificates.

Copy windows AD ca certificate which we exported in step 5 in /etc/openvpn directory. Export administrator or any other user certificate and key, by following step 6 and then copy the same in /etc/openvpn directory. Edit /etc/openvpn/server.conf file to change following -

ca RootCA.crt		#Windows AD CA certificate
cert administrator.crt	#Windows AD administrator certificate
key administrator.key	#Windows AD administrator key

Step 7: User authentication and certification validation.

Username and Password authentication
/etc/openvpn/server.conf
username-as-common-name
script-security 3
auth-user-pass-verify /etc/openvpn/scripts/auth.sh via-env

Certificate verification (Script to ensure users using only his/her creds and cert to access openvpn and user creds validation)

/etc/openvpn/scripts/auth.sh

#!/bin/bash

dn="cn=users,dc=vpn,dc=local"	#Change dc depends upon your AD domain
ad_host="10.136.60.58"		#Windows AD IP
ad_domain="vpn.local"		#Windows AD domain

if [ "${username,,}" != "${common_name,,}" ]; then
echo "$(date) | $username : DENIED  username [$username] and cert [$common_name] does not matched" >> /etc/openvpn/access.log
exit 1
fi

user=`ldapsearch -x -h $ad_host -b $dn -D "$username@$ad_domain" -w $password -s sub \
-b $dn "(&(objectCategory=person)(objectClass=user)(sAMAccountName=$username))" "dn" | grep 'numEntries:'`
if [ -z "$user" ]
then
    echo "$(date) | $username : Invalid password " >> /etc/openvpn/access.log
    exit 1
fi

echo "$(date) | $username : connected" >> /etc/openvpn/access.log
exit 0

Step 8: Setup OpenVpn server in HA (Active-Passive mode)

Assuming you have two OpenVpn servers already configured. Follow the given doc - HA Virtual IP (keepalived).docx

Change in /etc/openvpn/server.conf:-
local <your Virtual HA ip>	#Change it with your HA Virtual IP

Restart OpenVpn Server:-

$ service openvpn@server restart

Step 9: Change client ovpn file

remote <your Virtual HA ip> 1194
Add auth-user-pass
#Use AD certificates
ca RootCA.crt		#Windows AD CA certificate
cert administrator.crt	#Windows AD User certificate
key administrator.key	#Windows AD User key

Comment ns-cert-type server

#ns-cert-type server

Step 10: Ensure User will get same IP from both OpenVpn servers

Follow the given doc - How To Set Up and Configure NFS on Ubuntu 16.04.docx

Step 11: Restart the OpenVpn server
$ service openvpn@server restart