Since Magento 1.9.1 you can force HTTPS for the whole shop by adding the following configuration-snipped to /app/etc/config.xml or any module config.xml (own module!!!):

<frontend>
    <secure_url>
        <all>/</all>
    </secure_url>
</frontend>

After cleaning the config cache, Magento should generate secure URLs everywhere. That’s how to force secure URL’s in Magento.