This setup is for remote users to connect into an office/home LAN using a VPN (ipsec). This is based on (but not the same as) the strongSwan documentation and this guide: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_16.04.html
I used strongSwan 5.5.1.
apt-get install -y strongswan strongswan-pki