Automated IPSec/L2TP configuration

[wer...@gmail.com]

I want to develop a Vista client able to setup a VPN connection to a
Server with IP and PSK information gained from a SIP session. The
server supports both pure IPSec and IPSec/L2TP. Since we will be
behind a NAT device I presume pure IPSec wont work (KB 944335). I wish
there was a solution to this but I am looking at IPSec/L2TP right
now.

The question is; how to create a new IPsec/L2TP connection from a
client? We need to be able to configure IP, PSK and the supported
crypto-algorithm (this one might be optional). The server is a Linux
machine so we need a way to create and edit the connection using some
Vista API. I have looked at WFP but it seems to be at a lower level. I
found a IPSec Tunnel mode example (http://msdn.microsoft.com/en-us/
library/bb540651(VS.85).aspx) but if that won't work behind a NAT it
caanot be used. The best way would be if the API created the same
connection as if the "VPN connection wizard" was used.