I think you will have an easier time if you use CommandBox to spin up your server. It’s just as easy as Lucee express and far easier to configure. You can activate a self-signed cert just by doing
server set web.ssl.enable=true
server restart
Or you can configure a custom cert of your own.
However, if this is a local site and you have control over the code, I would simply modify the code that returns a 403 for testing purposes.