The Link Factory WordPress plugin is a backdoor. Distributed as a "homepage sentence publisher", it exposes an operator-controlled REST API under /wp-json/link-factory/v1/ - authenticated by a detached Ed25519 signature verified against a hardcoded operator public key (except for the health check).
https://wpscan.com/vulnerability/4cad269d-0146-4ca9-a1ae-55f02c8e5433/