Picking the font based on the browser – surely there's an open source plugin for NGINX or something that could replicate this? This is a perfect sort of thing

Picking the font based on the browser – surely there's an open source plugin for NGINX or something that could replicate this? This is a perfect sort of thing as a Caddy plugin too. Or a CDN provider to provide this out of the box. The CloudFlare people could do this in a weekend probably and I'd happily sign up because I'm less concerned about my privacy with CF than with Google. But is this even an issue? If you declare the 4 different formats, won't the browser know to request the best one automatically?