is_allowed_http_origin( null|string $origin = null )

function is_allowed_http_origin( $origin = null ) {
	$origin_arg = $origin;

	if ( null === $origin )
		$origin = get_http_origin();

	if ( $origin && ! in_array( $origin, get_allowed_http_origins() ) )
		$origin = '';

	/**
	 * Change the allowed HTTP origin result.
	 *
	 * @since WP-3.4.0
	 *
	 * @param string $origin     Origin URL if allowed, empty string if not.
	 * @param string $origin_arg Original origin string passed into is_allowed_http_origin function.
	 */
	return apply_filters( 'allowed_http_origin', $origin, $origin_arg );
}