Pantheon redirect environment to custom domain

pantheon-redirect-env-to-custom-domain.php

#Set the $base_url parameter if we are running on Pantheon: 

if (defined('PANTHEON_ENVIRONMENT')) {
	if (PANTHEON_ENVIRONMENT == 'dev') {
		$domain = 'sandbox.mysite.com'; 
	}
	else if (PANTHEON_ENVIRONMENT == 'test') {
		$domain = 'staging.mysite.com'; 
	} 
	else if (PANTHEON_ENVIRONMENT == 'live') {
		$domain = 'www.mysite.com'; 
	}
	else {
		# Fallback value for multidev or other environments. 
		# This covers environment-sitename.pantheonsite.io domains
		# that are generated per environment. 
		$domain = $SERVER_['HTTP_HOST'];
	}

	# This global variable determines the base for all URLs in Drupal. 
	$base_url = 'https://'. $domain; 
}