Eu entendi corretamente? Você quer estabelecer uma conexão VPN assim que fizer o login? Existe um pam -module que parece promissor:
pam-openvpnis a Linux PAM-module which works together with OpenVPN. With thispam-module it is possible to establish VPN connections when a user logs into a system and tear down the connection when the user logs off. This is ideal for mobile systems.