+'SessionCheckInfo': Validate a MediaWiki\Session\SessionInfo as it's being
+loaded from storage. Return false to prevent it from being used.
+&$reason: String rejection reason to be logged
+$info: MediaWiki\Session\SessionInfo being validated
+$request: WebRequest being loaded from
+$metadata: Array|false Metadata array for the MediaWiki\Session\Session
+$data: Array|false Data array for the MediaWiki\Session\Session
+
+'SessionMetadata': Add metadata to a session being saved.
+$backend: MediaWiki\Session\SessionBackend being saved.
+&$metadata: Array Metadata to be stored. Add new keys here.
+$requests: Array of WebRequests potentially being saved to. Generally 0-1 real
+ request and 0+ FauxRequests.
+