How to make a progressive web app on a LAN without https

I would like to make a progressive web app but for private use. What I mean is, I would like to serve the app from a LAN and have the app on the phone communicate with it on that same LAN. As far as I know, https is a requirement in order for the app to successfully be "installed" and for it to communicate with the server. Is there some method of allowing for this outside of generating a self-signed certificate? In other words, is there some exception allowing for the app to not have to use https if it is on the same network as the server?