set wordpress siteurl/home variable depending on HTTP_HOST

wp-config.php

# source : https://github.com/pantheon-systems/WordPress/blob/default/wp-config.php
# license : GPL 
# b2 is (c) 2001, 2002 Michel Valdrighi - m@tidakada.com -

if (isset($_SERVER['HTTP_HOST'])) {
    // HTTP is still the default scheme for now.
    $scheme = 'http';
    // If we have detected that the end use is HTTPS, make sure we pass that
    // through here, so <img> tags and the like don't generate mixed-mode
    // content warnings.
    if (isset($_SERVER['HTTP_USER_AGENT_HTTPS']) && $_SERVER['HTTP_USER_AGENT_HTTPS'] == 'ON') {
        $scheme = 'https';
        $_SERVER['HTTPS'] = 'on';
    }
    define('WP_HOME', $scheme . '://' . $_SERVER['HTTP_HOST']);
    define('WP_SITEURL', $scheme . '://' . $_SERVER['HTTP_HOST']);
}