Members area with one login/password for all members


I had created a website with a members-only area (including pages, a custom post type and a bbpress forum) but my client has decided they would like all members to be given the SAME password to access this area, and that this password should change at the end of every year. They do not want each member to have their own username/password (unless they want to take part in the forum).

I know I can individually password protect each page, but I’m not sure how this would work with the custom posts and the elements of the forum (inc keeping them out of search results)? Also, I don’t know if there would be a simple way to change the password at the year end?

I wonder if anyone has any ideas? Perhaps I should create a completely separate WordPress install for the ‘members area’ and protect this mini-site with a single password?

Any genius suggestions welcome!