password protect code

Hi i have a membership site. In the members area, my memeber click a link that connects them to a word press site. I want to protect the word press site from the public, i only want my members to have access not the public. I am not using word press to manage my members and I am not interested in doing that. I need a simple way of only allowing access to the word press site to people coming from the membership site. Here is the flow of how it works <[login to view URL]>