/ Network

VPN via NetworkManager

Fortinet SSL VPN

Install repository https://launchpad.net/~ar-lex/+archive/ubuntu/fortisslvpn

sudo add-apt-repository ppa:ar-lex/fortisslvpn              
sudo apt-get update

Install NetworkManager plugin plus UI

sudo apt install network-manager-fortisslvpn network-manager-fortisslvpn-gnome -y

A new VPN can be created with the GUI or dropping a file /etc/NetworkManager/system-connections/Company with chmod 0600 like this one :

[connection]
id=Company
uuid=129ad4ad-f3e9-4931-a377-4464454bcf546654
type=vpn
autoconnect=false
permissions=user:your_unix_user:;
secondaries=

[vpn]
gateway=vpn.company.com:443
user=rgarrigue
trusted-cert=4939499ef9235465465465465ee165141c00f8ce0068fa4988252884b42136466362a07e
password-flags=1
service-type=org.freedesktop.NetworkManager.fortisslvpn

[ipv4]
dns-search=
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=ignore

To get the cert=4939499ef9235465465465465ee165141c00f8ce0068fa4988252884b42136466362a07e part, one way is to configure the VPN without, try to connect, fail, then have a look in /var/log/syslog (on Ubuntu), there'll be something like this with the required ID.

Oct 27 15:20:36 your_pc NetworkManager[1170]: <info>  [1509110436.7548] vpn-connection[0x1f96210,129ad4ad-f3e9-4931-a377-2c7b44a47340,"Company",0]: VPN plugin: state changed: starting (3)
Oct 27 15:20:36 your_pc NetworkManager[1170]: ERROR:  Gateway certificate validation failed, and the certificate digest in not in the local whitelist. If you trust it, rerun with:
Oct 27 15:20:36 your_pc NetworkManager[1170]: ERROR:      --trusted-cert 4939499ef9235465465465465ee165141c00f8ce0068fa4988252884b42136466362a07e
Oct 27 15:20:36 your_pc NetworkManager[1170]: ERROR:  or add this line to your config file:
Oct 27 15:20:36 your_pc NetworkManager[1170]: ERROR:      trusted-cert = 4939499ef9235465465465465ee165141c00f8ce0068fa4988252884b42136466362a07e