Workaround for redirects with WordPress HTTPS and WordPress MU Domain Mapping

wordpress_https_workaround.php

<?php
/*
Plugin Name: Workaround for HTTPS with Domain Mapping
Description: Disables redirect from MU Domain Mapping Plugin on SSL-secured pages
Author: Thomas Ulrich
Author URI: https://github.com/JustThomas
Version: 0.1
*/

function tu_wordpress_https_workaround() {
	if( is_ssl() && class_exists('WordPressHTTPS') && function_exists('domain_mapping_siteurl') ) {
		global $wordpress_https;
		if( is_a( $wordpress_https, 'WordPressHTTPS' ) ) {			
			/*
			 * The page has been requested through HTTPS, the
			 * WordPress HTTPS plugin is active and a SSL host is
			 * set in the plugin settings
			 * Therefore, prevent the Domain Mapping plugin from 
			 * redirecting to the primary domain.
			 */
			if ( remove_action( 'template_redirect', 'redirect_to_mapped_domain' ) ) { 
				// Redirect to HTTPS using WordPress HTTPS
				$wordpress_https->redirect('https');
			}
		}
	}
}
/*
 * 'priority' parameter has to be smaller than 10. Otherwise, the
 * domain mapping redirect will fire before this workaround kicks in
 */
add_action( 'template_redirect', 'tu_wordpress_https_workaround', 9);

function tu_remove_dm_admin_redirect() {
	if( is_ssl() && class_exists('WordPressHTTPS') && function_exists('domain_mapping_siteurl') ) {
		global $wordpress_https;
		if( is_a( $wordpress_https, 'WordPressHTTPS' ) ) {			
			remove_action('admin_init', 'dm_redirect_admin');
		}
	}
}
add_action( 'admin_init', 'tu_remove_dm_admin_redirect', 9 );