Pantheon HTTPS and www hostname redirects for WordPress config

wp-config.php

<?php
// wp-config.php snippet. Put this just before the "Happing Pressing!" comment.


// HTTPS and www redirects.
// Edit constants below based on your needs.
define( 'HOSTNAME_PREFERRED', 'www.domain.com' );
define( 'HOSTNAME_PANTHEON_LIVE', 'live-domain.pantheonsite.io' );
define( 'FORCE_HTTPS', true );

// Probably don't edit this part, uses the constants to do expected things.
if ( isset( $_SERVER['PANTHEON_ENVIRONMENT'] ) &&
	php_sapi_name() !== 'cli' ) {

	// Force HTTPS on for ALL Pantheon Environments.
	if ( FORCE_HTTPS && ( ! isset( $_SERVER['HTTP_X_SSL'] ) && 'https' !== $_SERVER['HTTP_X_FORWARDED_PROTO'] ) ||
	( isset( $_SERVER['HTTP_X_SSL'] ) && 'ON' !== $_SERVER['HTTP_X_SSL'] ) ) {
		header( 'HTTP/1.0 301 Moved Permanently' );
		header( 'Location: https://'. $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] );
		exit();
	}
	// Force preferred hostname for live/prod site, except the Pantheon
	// default hostname -- leave that working in case of emergency.
	if ( 'live' === $_SERVER['PANTHEON_ENVIRONMENT'] ) {
		if ( HOSTNAME_PREFERRED !== $_SERVER['HTTP_HOST'] &&
			HOSTNAME_PANTHEON_LIVE !== $_SERVER['HTTP_HOST'] ) {
			if ( FORCE_HTTPS ) {
				$scheme = 'https://';
			} else {
				$scheme = 'http://';
			}
			$location = $scheme . HOSTNAME_PREFERRED . $_SERVER['REQUEST_URI'];
			// Issue the redirect.
			header( 'HTTP/1.0 301 Moved Permanently' );
			header( "Location: $location" );
			exit();
		}
	}
}