I'm not sure what Steady is, but it sounds like FreshRSS can do what you want. If you can read the articles on the website, then you should be able to use FreshRSS to scrape the site and create a feed from it. For content behind a login, I'm pretty sure FreshRSS can handle basic-auth or you can provide it cookies.
There's also KillTheNewsLetter which does what you want the other way, by just converting the emails into an RSS feed. It can be self-hosted, but I haven't tried it myself, though.