needs a GINA replacement for this - maybe some can remember the novell-client, that's acting that way... never heared about a GINA for openvpn - unfortunately... cheers
first you would have to use a certificate based system and not a username-password based one for openvpn. I do not know if astaro suports se3cure certificates for it's openvpn or not. Then you need to start openvpn as a service.