原文(source): .htaccess – How do I force HTTPS on a single file? (PHP) – Stack Overflow
At the beginning of the PHP page that does all your credit card processing, you can add this:
It will redirect back to itself, except using https if it was first loaded over http. Of course you still need an SSL certificate installed for your domain.
if(!isset($_SERVER['HTTPS'])||!$_SERVER['HTTPS']){// if request is not secure, redirect to secure url
$url ='https://'. $_SERVER['HTTP_HOST']. $_SERVER['REQUEST_URI'];
header('Location: '. $url);
exit;
}