@andypiper well, most challenging is to work around unicode (#DOjS and therefore #DOStodon do not support unicode) and to support TLS.
the later is less a problem of the API but more of how the HTTP servers are configured.

Also: media types are problematic. Theoretically I could play back GIF animations, but because these are served as mp4 in Mastodon I can't do anything sensible.
Serving webp or other 'modern' image formats would be problematic as well...