MU-Plugin to force SSL for a specific WordPress page

force-ssl.php

<?php
/**
 * Plugin Name: SSL Redirect
 * Description: Redirects a specific page to HTTPS
 */
if ( ! function_exists( 'force_https' ) ) {
	function force_https() {
		if ( is_page( 'some-page-slug-here' ) && !is_ssl() ) {
			wp_redirect('https://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'], 301 );
			exit();
		}
	}
	add_action ( 'template_redirect', 'force_https', 1 );
}