Add web account AT Protocol

[tynanpurdy]

I propose adding an integration with the AT Protocol to import RSS subscriptions from Leaflet.pub, a blogging platform on the Atmosphere. Leaflet serves blogs over RSS, as well as allowing Bluesky/AT Proto accounts to subcribe to individual publications. I would find an integration incredibly useful if it could pull all of my Leaflet subscriptions into NetNewsWire.

I've mocked up what this integration could look like. On a technical level, authentication is not really necessary as this would be a mostly read-only integration. If a user wanted to unsubscribe from a Leaflet publication by removing it from NNW, then that would require authentication. I've also hinted at the possibility of other kinds of RSS feeds that could be discovered by an ATproto account, such as Tangled (a git forge with ATproto social layer) repos that have been starred. An MVP would focus on Leaflet, but other expansions such as Tangled are equally feasible.

Technical details

A user repository with Leaflet subscriptions will have a collection of pub.leaflet.graph.subscription records. See an example of such a record here. That record links to the URI of a publication record (see example). The publication has a base_path field which specifies the URL of the publication. Simply append /rss to that URL and you have the feed. A simple integration would take an account handle, resolve the location of the repository, and gather the base_path of each subscription record.

With authentication, removing the feed from NNW could trigger the deletion of the corresponding pub.leaflet.graph.subscription record.

Mockup