How to guard a website/app behind VPN network

Hi,

I’m developing a NextJS web app and I want to setup a dev env such that there’s always a up-to-date application reading from the github repo.

However, since it’s the dev branch, I want to it only be accessed if the request is ona VPN.

My plan

• 1. Setup a VPN service in a droplet (solved, there’s tutorial)
• 2. Deploy an app such that it’s only accessible when on that VPN (? not sure how to achieve this)

I imagine i can do some IP check in NextJS? but wondering if there’s more elegant solution like setup the firewall on 2)'s droplet (I guess I cannot just deploy it through the App product)

Wondering if anyone did similar and can offer some input. Thanks