http://gpp6nwvsps43b3mfacsh433uroo6uyjvvpr6tgj4jh4n5ngxt7rqbvid.onion/posts/ikev2-libreswan.html
When you are asked about the usage, enter 0 for digital signature, then 2 for key encipherment, then anything else to end. When asked if this is a critical extension, enter n for no. When you are asked about the extended key usage, enter 0 for server authentication, 1 for client authentication, then anything else to end.