Connect to FortigateVPN with OpenfortiVPN

I've got a lot of feedback for my old article How to connect to a FortiGate IPSec-VPN using Linux. However, the connection with vpnc was never stable for me, it always segfaults after a while and I had to restart it.

So I did some more research and found a relative new project called openfortivpn by Adrien Vergé, which uses the SSL VPN tunnel feature of Fortigate instead of IPSec. Additionally, NetworkManager support already exists thanks to the Gnome people.