We are not anyhow affililated to Outine and its company. Outline is a VPN. Not exactly an addon but you can control the restrict the accesses to your VPS or server if you have a permant static IP address.
As you do not pay for using outline, but only to Digial Ocean or Google to create a VPN server cost as little as USD5 if you have chosen digital ocean. Digital Ocean offers a choice of 8 countries where you can set up the outline VPN server.
They claim that no data is collected. I felt it is safer and more stable using outline VPN. Once, I was trying a dedicated IP VPN from one of the VPN service provider, my firewall detected port scanning, To find out more, visit their website. No discount for this item, just recommendation.