Support http and https concurrently in wp-config

M&D wp-config.php

<?php

/**
 * Determine if the current request is SSL. Set $_SERVER['HTTPS'] for WordPress' build in is_ssl().
 *
 * @return True if the site uses ssl directly or through a load balancer
 */
function greenpeace_is_ssl() {
        $is_ssl = (isset( $_SERVER['HTTPS'] ) && 'on' === $_SERVER['HTTPS'] )
        || (isset( $_SERVER['HTTP_X_FORWARDED_PROTO'] ) && 'https' === $_SERVER['HTTP_X_FORWARDED_PROTO'])
        || $_SERVER['SERVER_PORT'] == 443;

        // https://codex.wordpress.org/Function_Reference/is_ssl
        // Set the server HTTPS flag for WP's built in is_ssl() function
        if ( $is_ssl ) {
                $_SERVER['HTTPS'] = 'on';
        }

        return $is_ssl;
}

$web_site     = $_SERVER['HTTP_HOST'];
$schema       = greenpeace_is_ssl() ? 'https://' : 'http://';
$web_site_url = $schema . $web_site;

define( 'WP_HOME',    $web_site_url );
define( 'WP_SITEURL', $web_site_url );