enable secure site only on certain pages
I have two options, but there could be more (quotes included are from their project pages):


Secure Pages:


  A small process which will redirect the required pages to a SSL version of the page.

Context SSL:


  Allow site administrators to make sure certain sections of their sites are always accessed through SSL.
  
  This module adds a reaction plugin to the Context module and thus benefits from all the flexibility that the Context module provides.