Sunrise to allow different domains for administration on a Wordpress multi-site blog

sunrise.php

<?php
/**
 * File sunrise.php
 *
 * This file is read and run before most of wordpress functionality. Here we will allow
 * all multi-site blogs administration interfaces to work on another domain (usually inside
 * a VPN).
 */
if (!function_exists('sunrise_modify_domain')):
        /**
         * Replaces the origin domain with the masked domain. This uses the constants
         * `WP_MASKED_DOMAIN` and `DOMAIN_CURRRENT_SITE` to replace the string.
         *
         * @param string $url           Full URL to replace the domain.
         *
         * @return string The replaced string. If constants are not defined, it will return the original url.
         */
        function sunrise_modify_domain($url) {
                global $current_domain;
                if (defined('WP_MASKED_DOMAIN') and defined('DOMAIN_CURRENT_SITE')) {
                        return str_replace(DOMAIN_CURRENT_SITE, $current_domain, $url);
                } else {
                        return $url;
                }
        }
endif;

/**
 * We limit this functionality only when using administration interface. Also, constant
 * `WP_MASKED_DOMAIN` must be defined as an array of possible alternative domains. If you
 * want *all domains*, use `$_SERVER['HTTP_HOST']` as a value in this array.
 */
if (
    (defined('WP_MASKED_DOMAIN') and defined('DOMAIN_CURRENT_SITE')) and
    (is_admin() or preg_match('/^\/([^\/]+\/)?(wp-login\.php|wp-json\/|wp-content\/)/', $_SERVER['REQUEST_URI']))
   ) {
        $current_domain = strtolower(stripslashes($_SERVER['HTTP_HOST']));

        if (str_ends_with($current_domain, ':80')) {
                $current_domain = substr($domain, 0, -3);
                $_SERVER['HTTP_HOST'] = substr($_SERVER['HTTP_HOST'], 0, -3);
        } elseif (str_ends_with($current_domain, ':443')) {
                $current_domain = substr($domain, 0, -4);
                $_SERVER['HTTP_HOST'] = substr($_SERVER['HTTP_HOST'], 0, -4);
        }

        if (in_array($current_domain, WP_MASKED_DOMAIN)) {
                $current_path = stripslashes($_SERVER['REQUEST_URI']);
                $blog_path = preg_replace('/^(\/[^\/]+\/).*/', '\1', $current_path);
                $blog_path = rtrim($blog_path, '/');
                $blog_path = $blog_path . '/';

                $blog_id = $wpdb->get_var(
                        $wpdb->prepare("SELECT blog_id FROM $wpdb->blogs WHERE domain = %s and path = %s", DOMAIN_CURRENT_SITE, $blog_path));

                if ($blog_id === null) {
                        $blog_id = $wpdb->get_var(
                                $wpdb->prepare("SELECT blog_id FROM $wpdb->blogs WHERE domain = %s and path = %s", DOMAIN_CURRENT_SITE, '/'));
                }

                $current_site = get_network(1);
                $current_blog = get_site($blog_id);

                add_filter('home_url', 'sunrise_modify_domain', 100, 1);
                add_filter('site_url', 'sunrise_modify_domain', 100, 1);
                //add_filter('upload_dir', 'sunrise_modify_domain', 10);
                //add_filter('the_content', 'sunrise_modify_domain', 100, 1);
                //add_filter('content_url', 'sunrise_modify_domain', 100, 1);
                //add_filter(‘pre_option_home’, ‘dev_pre_url_filter’, 1 );
                //add_filter(‘pre_option_siteurl’, ‘dev_pre_url_filter’, 1 );
                //add_filter(‘post_thumbnail_html’, ‘dev_content_filter’, 100 );
                //add_filter(‘wp_get_attachment_link’, ‘dev_content_filter’, 100 );
                //add_filter(‘wp_get_attachment_url’, ‘dev_content_filter’, 100 );
        }
}

/*
// some hardass debugging...
echo "<p>current_domain: " . $current_domain . "</p>\n";
echo "<p>current_path: " . $current_path . "</p>\n";
echo "<p>blog_path: " . $blog_path . "</p>\n";
echo "<p>blog_id: " . $blog_id . "</p>\n";
echo "<p>current_site: "; var_dump($current_site); echo "</p>\n";
echo "<p>current_blog: "; var_dump($current_blog); echo "</p>\n";
exit();
*/

References:

• https://stackoverflow.com/questions/48510333/wordpress-multisite-and-single-database-for-all-developers
• https://www.hallaminternet.com/wordpress-multisite-local-remote-development/
• https://403.ie/how-to-serve-wp-admin-from-a-separate-subdomain/
• https://docs.wpvip.com/wordpress-on-vip/multisites/multiple-domains/