Add option to support user/password http basic auth or other security options

Would it be possible to add basic http auth to the http server such that a user/pass can be configured?

Other possible options could include generating a long token that's entered when you first open the page and can be shown via an additional vim command.

Currently I'm trying to use markdown-preview.nvim via `mkdp_open_to_the_world` with a local browser while the vim session is running on a remote machine. This all works but hoping for a better way to lock it down. Otherwise I might try to put a proxying web server in front of this.