wordpress-activitypub/includes/rest/class-webfinger.php

<?php
namespace Activitypub\Rest;

/**
 * ActivityPub WebFinger REST-Class
 *
 * @author Matthias Pfefferle
 *
 * @see https://webfinger.net/
 */
class Webfinger {
	/**
	 * Initialize the class, registering WordPress hooks
	 */
	public static function init() {
		\add_action( 'rest_api_init', array( '\Activitypub\Rest\Webfinger', 'register_routes' ) );
		\add_action( 'webfinger_user_data', array( '\Activitypub\Rest\Webfinger', 'add_webfinger_discovery' ), 10, 3 );
	}

	/**
	 * Register routes
	 */
	public static function register_routes() {
		\register_rest_route(
			'activitypub/1.0',
			'/webfinger',
			array(
				array(
					'methods'             => \WP_REST_Server::READABLE,
					'callback'            => array( '\Activitypub\Rest\Webfinger', 'webfinger' ),
					'args'                => self::request_parameters(),
					'permission_callback' => '__return_true',
				),
			)
		);
	}

	/**
	 * Render JRD file
	 *
	 * @param  WP_REST_Request   $request
	 * @return WP_REST_Response
	 */
	public static function webfinger( $request ) {
		$resource = $request->get_param( 'resource' );

		$matched = \str_contains( $resource, '@' );

		if ( ! $matched ) {
			return new \WP_Error( 'activitypub_unsupported_resource', \__( 'Resource is invalid', 'activitypub' ), array( 'status' => 400 ) );
		}

		$resource = \str_replace( 'acct:', '', $resource );

		$resource_identifier = \substr( $resource, 0, \strrpos( $resource, '@' ) );
		$resource_host = \substr( \strrchr( $resource, '@' ), 1 );

		if ( \wp_parse_url( \home_url( '/' ), \PHP_URL_HOST ) !== $resource_host ) {
			return new \WP_Error( 'activitypub_wrong_host', \__( 'Resource host does not match blog host', 'activitypub' ), array( 'status' => 404 ) );
		}

		$user = \get_user_by( 'login', \esc_sql( $resource_identifier ) );

		if ( ! $user ) {
			return new \WP_Error( 'activitypub_user_not_found', \__( 'User not found', 'activitypub' ), array( 'status' => 404 ) );
		}

		$json = array(
			'subject' => $resource,
			'aliases' => array(
				\get_author_posts_url( $user->ID ),
			),
			'links' => array(
				array(
					'rel'  => 'self',
					'type' => 'application/activity+json',
					'href' => \get_author_posts_url( $user->ID ),
				),
				array(
					'rel'  => 'http://webfinger.net/rel/profile-page',
					'type' => 'text/html',
					'href' => \get_author_posts_url( $user->ID ),
				),
			),
		);

		return new \WP_REST_Response( $json, 200 );
	}

	/**
	 * The supported parameters
	 *
	 * @return array list of parameters
	 */
	public static function request_parameters() {
		$params = array();

		$params['resource'] = array(
			'required' => true,
			'type' => 'string',
			'pattern' => '^acct:(.+)@(.+)$',
		);

		return $params;
	}

	/**
	 * Add WebFinger discovery links
	 *
	 * @param array   $array    the jrd array
	 * @param string  $resource the WebFinger resource
	 * @param WP_User $user     the WordPress user
	 */
	public static function add_webfinger_discovery( $array, $resource, $user ) {
		$array['links'][] = array(
			'rel'  => 'self',
			'type' => 'application/activity+json',
			'href' => \get_author_posts_url( $user->ID ),
		);

		return $array;
	}

	public static function resolve( $account ) {
		if ( ! preg_match( '/^@?[^@]+@((?:[a-z0-9-]+\.)+[a-z]+)$/i', $account, $m ) ) {
			return null;
		}
		$url = \add_query_arg( 'resource', 'acct:' . ltrim( $account, '@' ), 'https://' . $m[1] . '/.well-known/webfinger' );
		if ( ! \wp_http_validate_url( $url ) ) {
			return new \WP_Error( 'invalid_webfinger_url', null, $url );
		}

		// try to access author URL
		$response = \wp_remote_get(
			$url,
			array(
				'headers' => array( 'Accept' => 'application/activity+json' ),
				'redirection' => 0,
			)
		);

		if ( \is_wp_error( $response ) ) {
			return new \WP_Error( 'webfinger_url_not_accessible', null, $url );
		}

		$response_code = \wp_remote_retrieve_response_code( $response );

		$body = \wp_remote_retrieve_body( $response );
		$body = \json_decode( $body, true );

		if ( ! isset( $body['links'] ) ) {
			return new \WP_Error( 'webfinger_url_invalid_response', null, $url );
		}

		foreach ( $body['links'] as $link ) {
			if ( $link['rel'] === 'self' && $link['type'] == 'application/activity+json' ) {
				return $link['href'];
			}
		}

		return new \WP_Error( 'webfinger_url_no_activity_pub', null, $body );
	}
}