It's easy to do. Here are some examples: https://www.packetizer.com/ws/webfinger/server.html

I actually serve up content using both static files and via dynamically generated content, depending on the domain and needs.

Those are steps for running a server with rules engine. I don’t want a server, I want users to be able to access a CDN directly which may not have such flexible rewrite rules. I’m building a kind of bluesky alt that works entirely statically and should be flexible to file hosting