The setup of the Internet login for Linux/Unix has multiple possible configurations. First of all you can select between PPTP VPN and OpenVPN. A comparison can be found under PPTP VPN and OpenVPN access.
If you would like to use PPTP VPN, please follow the link below. PPTP VPN is supported well under Linux.
For other unix variants like FreeBSD, OpenBSD, Solaris and so on you should use the OpenVPN protocol: