kb-fediverse-webfinger-discovery

To find a WebFinger handle from an ActivityPub actor URL, you use reverse WebFinger discovery defined in FEP-2c59. This resolves the actor URL to its corresponding human-readable WebFinger address, ensuring reliable cross-platform identity verification.

FEP-2c59 is a Fediverse Enhancement Proposal that standardizes reverse WebFinger discovery. It defines the `webfinger` property used to resolve ActivityPub actor URLs back to their corresponding WebFinger addresses, addressing inconsistencies across different platforms.

Handling domain mismatches requires checking the `webfinger` property on the actor URL to correctly identify WebFinger addresses hosted on a different domain than the ActivityPub server. FEP-2c59 provides the mechanism to bridge these cross-domain identity scenarios.

Validating a discovered WebFinger address involves resolving it back to the original ActivityPub actor URL. The validation ensures the discovered address correctly resolves without redirects, confirming the identity link is legitimate and unbroken.

Mastodon currently uses its own approach to WebFinger discovery rather than strictly implementing FEP-2c59. This Skill analyzes Mastodon's current method and highlights ongoing community debates regarding alternative solutions for resolving actor URLs.