Publicize: add Fediverse meta tag on posts when available

See https://blog.joinmastodon.org/2024/07/highlighting-journalism-on-mastodon/

If we have an existing Mastodon connection on the site, let's add it as meta tag on each post.

projects/packages/publicize/changelog/add-fediverse-tag-social

@@ -0,0 +1,4 @@
+Significance: patch
+Type: added
+
+Mastodon: display a Fediverse Creator tag when the post author has connected their account to a Mastodon account.

projects/packages/publicize/package.json

@@ -1,7 +1,7 @@
 {
 	"private": true,
 	"name": "@automattic/jetpack-publicize",
-	"version": "0.47.1",
+	"version": "0.47.2-alpha",
 	"description": "Publicize makes it easy to share your site’s posts on several social media networks automatically when you publish a new post.",
 	"homepage": "https://github.com/Automattic/jetpack/tree/HEAD/projects/packages/publicize/#readme",
 	"bugs": {

projects/packages/publicize/src/class-publicize-base.php

@@ -254,6 +254,10 @@ public function __construct() {
 		// The custom priority for this action ensures that any existing code that
 		// removes post-thumbnails support during 'init' continues to work.
 		add_action( 'init', __NAMESPACE__ . '\add_theme_post_thumbnails_support', 8 );
+
+		// Add a Fediverse Open Graph Tag when an author has connected their Mastodon account.
+		add_filter( 'jetpack_open_graph_tags', array( $this, 'add_fediverse_creator_open_graph_tag' ), 10, 1 );
+		add_filter( 'jetpack_open_graph_output', array( $this, 'filter_fediverse_cards_output' ), 10, 1 );
 	}
 
 	/**
@@ -2128,6 +2132,50 @@ public function get_dismissed_notices() {
 	public static function can_manage_connection( $connection_data ) {
 		return current_user_can( 'edit_others_posts' ) || get_current_user_id() === (int) $connection_data['user_id'];
 	}
+
+	/**
+	 * Display a Fediverse actor Open Graph tag when the post author has a Mastodon connection.
+	 *
+	 * @see https://blog.joinmastodon.org/2024/07/highlighting-journalism-on-mastodon/
+	 *
+	 * @param array $tags Current tags.
+	 *
+	 * @return array
+	 */
+	public function add_fediverse_creator_open_graph_tag( $tags ) {
+		if ( ! is_singular() ) {
+			return $tags;
+		}
+
+		// Loop through active connections.
+		foreach ( (array) $this->get_services( 'connected' ) as $service_name => $connections ) {
+			if ( 'mastodon' !== $service_name ) {
+				continue;
+			}
+
+			// services have multiple connections.
+			foreach ( $connections as $connection ) {
+				if ( ! empty( $connection['external_display'] ) ) {
+					$tags['fediverse:creator'] = esc_attr( $connection['external_display'] );
+				}
+				break;
+			}
+		}
+
+		return $tags;
+	}
+
+	/**
+	 * Update the markup for the Open Graph tag to match the expected output for Mastodon
+	 * (name instead of property).
+	 *
+	 * @param string $og_tag A single OG tag.
+	 *
+	 * @return string Result of the OG tag.
+	 */
+	public static function filter_fediverse_cards_output( $og_tag ) {
+		return ( str_contains( $og_tag, 'fediverse:' ) ) ? preg_replace( '/property="([^"]+)"/', 'name="\1"', $og_tag ) : $og_tag;
+	}
 }
 
 // phpcs:disable Universal.Files.SeparateFunctionsFromOO.Mixed -- TODO: Move these functions to some other file.