I've been developing an #ActivityPub C2S-based (with extensions) API facade/proxy proof-of-concept for Mastodon. It runs as a separate process that supports proxying the Masto operations but also adds a postable C2S outbox with support for AP C2S activities. These activities are converted into upstream Mastodon API calls. This extended C2S API also supports search, streaming events, managing bookmark collections, and retrieving timeline collections. 1/2