In case you need to force HTTPS on every single page of a WordPress site, here's how.

force-http-wordpress.php

<?php
 
$using_ssl = isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on' || $_SERVER['SERVER_PORT'] == 443;
add_action('wp', 'check_ssl');
function check_ssl()
{
    // All pages must be https. Redirect to https if not already
    if (! $using_ssl)
    {
        header('HTTP/1.1 301 Moved Permanently');
        header('Location: https://' . $_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI']);
        exit;
    }
}
 
?>