default-cache-control.php

<?php
/**
 * Plugin Name: Be API - Cache-control
 * Description: Add must-revalidate to the cache-control directive.
 * Version: 1.0
 * Author: BE API Technical team
 * Author URI: https://www.beapi.fr
 */

namespace BEAPI\Plugin_Defaults\cache_control;

add_action( 'plugins_loaded', __NAMESPACE__ . '\\cache_control_default_settings' );

/**
 * Add default setting for the cache control plugin
 */
function cache_control_default_settings() {
	global $cache_control_options;

	if ( empty( $cache_control_options ) ) {
		return;
	}

	foreach ( $cache_control_options as $index => $options ) {
		$options['s_maxage'] = $options['max_age'];
		$options['max_age']  = 0;

		// On Server error, the page can be served 3 times the original value
		$options['staleerror'] = $options['s_maxage'] * 3;

		// The stored by Varnish will be served for 5 times the original value even if the page is expired.
		// Server will get the new version as soon as one new user get it.
		$options['stalereval']           = $options['s_maxage'] * 5;
		$cache_control_options[ $index ] = $options;
	}
}