https://github.com/discourse/discourse-activity-pub is a plugin for Discourse that adds basic ActivityPub support.

It still misses some important features. One of such is webfinger support.

Webfinger is a feature that lets you take any ActivityPub-enabled content - say, a video on Peertube like https://video.internet-czas-dzialac.pl/w/fHG7PsFJuqwzA4ByQYQ6Re, take its URL from the browser bar, and paste it into the search field of a fediverse app like Mastodon in order to view it in that fediverse app:

Currently you cannot do that with a Discourse topic. If you take an ActivityPub-enabled Discourse instance topic, like https://forum.internet-czas-dzialac.pl/t/otwieramy-forum-activitypub/2683, and paste it into Mastodon search, it yields no results:

If we add webfinger support for the topic URL in Discourse Activity Pub plugin, then that search functionality will work. This is what this task is about