how do I make a specific page SSL secured with a specific subdomain
===

I have my website and the page that I accept credit cards I want to have SSL. I got my SSL all setup for the subdomain: secure.website.com

So, how do I make sure that the page I accept credit cards on always is https and has a subdomain of secure.website.com. 

The address is: http://www.website.com/subscriptions/new 

and that needs to be

https://secure.website.com/subscriptions/new

how do I make it always render that URL?