Stop automatic redirect from https://www.mysite.com -> http://www.mysite.com

I have implemented a action method (in my plugin folder which handles user login functionality) which checks if a valid user has logged in and if yes, redirects them to https://www.mysite.com (https will be used for logged in users).

Problem is, accessing https://www.mysite.com directly causes a redirect to the non-https version: http://www.mysite.com … which then causes an infinite loop to occur.

So I was wondering – how to stop https://www.mysite.com redirecting automatically to: http://www.mysite.com?

Many thanks for any help,
gvanto