You are right, steamworks definitely is more widely used extension and I changed the http requests to use it instead and made some other changes aswell.
Code:
1.1.0 (17-Jan-2019)
- Made the plugin use steamworks instead of system2 for http requests.
- Added option to change the url which is used to check for vpns.
- Added option to only log users who join with VPN instead of kicking them.