- [FEP-3b86: Activity Intents](https://codeberg.org/fediverse/fep/src/branch/main/fep/3b86/fep-3b86.md): offer handlers for `Object` and `Create` (with support for the `content` parameter only), has support for the `Follow`, `Announce`, `Like` and `Object` intents
Mastodon largely follows the ActivityPub server-to-server specification but it makes uses of some non-standard extensions, some of which are required for interacting with Mastodon at all.
In Mastodon, users are identified by a `username` and `domain` pair (e.g., `Gargron@mastodon.social`).
This is used both for discovery and for unambiguously mentioning users across the fediverse. Furthermore, this is part of Mastodon's database design from its very beginnings.
As a result, Mastodon requires that each ActivityPub actor uniquely maps back to an `acct:` URI that can be resolved via WebFinger.
In order to authenticate activities, Mastodon relies on HTTP Signatures, signing every `POST` and `GET` request to other ActivityPub implementations on behalf of the user authoring an activity (for `POST` requests) or an actor representing the Mastodon server itself (for most `GET` requests).
Mastodon requires all `POST` requests to be signed, and MAY require `GET` requests to be signed, depending on the configuration of the Mastodon server.
These limits are intended to be very generous and way above what the Mastodon user experience is optimized for, so as to accommodate future changes and unusual or unforeseen usage patterns, while still providing some limits for performance reasons.
