Normally, the security of a VPN is based on a X.509 certificate / private key pair, which all users of the VPN must possess in order to gain access. The security of your VPN can be further increased by requiring users to also supply a username and password when they connect to the OpenVPN server.
On the server side, the verification of the username and password can be done using several mechanisms:
Using a server-side password file that contains the username and their hashed passwords.
It is also possible to authenticate against a Windows Active Directory domain, as this is very similar to using a standalone LDAP server. In this example, we will show you...