Generate trusted developer certs for your local machine. I personally keep copies of my generated certs in ~/docs/mkcert.

git clone https://github.com/FiloSottile/mkcert && cd mkcert
go build -ldflags "-X main.Version=$(git describe --tags)"

Create a fake certificate authority and configure it for your browsers:
mkcert -install

Create and sign certificates:
mkcert example.com localhost 127.0.0.1 ::1

Uninstall it with:
mkcert -uninstall

void linux

Automatic RootCA installation isn't supported on void linux (it still installs for Firefox and Chrome, but many other programs use the system's certificates).

It turns out creating this directory and re-running mkcert -install works:
/usr/local/share/ca-certificates

If that doesn't work you can just manually copy the cert into that directory. Worst case scenario check out man update-ca-certificates for the more annoying way.