gistfile1.txt

$ sudo cat /etc/NetworkManager/system-connections/foo.nmconnection
[sudo] password for grahamc:
[connection]
id=foo
uuid=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
type=vpn
autoconnect=false
permissions=

[vpn]
gateway=x.xx.xx.xxx
ipsec-enabled=yes
ipsec-esp=3des-sha1!
ipsec-ike=3des-sha1-modp1024!
ipsec-psk=0sbase64encodedsctringgoeshere
mru=1400
mtu=1400
password-flags=0
user=graham@xxxxxxxxxxxxx
service-type=org.freedesktop.NetworkManager.l2tp

[vpn-secrets]
password=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

[ipv4]
dns-search=
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=
ip6-privacy=0
method=auto