Example transformer to add a "nonce" attribute to script tags in stories

web-stories-csp-nonce-transformer.php

<?php
/**
 * Plugin Name: Web Stories CSP nonce transformer example
 * Description: Example transformer to add a "nonce" attribute to script tags in stories.
 * Author: Pascal Birchler
 * Author URI: https://pascalbirchler.com/
 * Version: 0.0.1
 * Requires at least: 6.4
 * Requires PHP: 7.4
 * License: Apache License 2.0
 * License URI: https://www.apache.org/licenses/LICENSE-2.0
 *
 * @copyright 2023 Google LLC
 * @license   https://www.apache.org/licenses/LICENSE-2.0 Apache License 2.0
 */


if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

add_action(
	'init',
	static function() {
		if ( ! interface_exists( '\Google\Web_Stories_Dependencies\AmpProject\Optimizer\Transformer' ) ) {
			return;
		}

		add_filter(
			'web_stories_amp_optimizer_config',
			static function ( $config ) {
				$config['transformers'][] = Your_Website_Example_CSP_Nonce_Transformer::class;
				return $config;
			}
		);

		class Your_Website_Example_CSP_Nonce_Transformer implements \Google\Web_Stories_Dependencies\AmpProject\Optimizer\Transformer {
			public function transform( \Google\Web_Stories_Dependencies\AmpProject\Dom\Document $document, \Google\Web_Stories_Dependencies\AmpProject\Optimizer\ErrorCollection $errors ) {
				$scripts = $document->xpath->query( '//script[ not( @type ) or @type = "module" ]' );
				foreach ( $scripts as $script ) {
					/** @type \DOMElement $script */
					$script->setAttribute( 'nonce', 'fooo' );
				}
			}
		}
	}
);