$ sudo apt install openfortivpn
$ touch openfortivpn.conf
$ chmod go= openfortivpn.conf

host =
port =
username =
password =
# trusted-cert =

$ sudo openfortivpn -c openfortivpn.conf
ERROR:  Gateway certificate validation failed, and the certificate digest in not in the local whitelist. If you trust it, rerun with:
ERROR:      --trusted-cert  <some-random-string-to-add-to-trusted-cert>

sudo openfortivpn -c openfortivpn.conf

sudo openfortivpn -u <USER> -p <PASSWORD> --trusted-cert <CERTIFICATE> <SERVER>:<PORT>