How to get a list of all classes that inherit from BasePage in the web-application.

I need to get a list of all of these webforms.
As the subject reads, how can i accomplish this ? All my webforms inherits from a class called "BasePage".
It can also suffice with only getting a list of all the webforms in the application, regardless of base class since i can check inheritance later in code.

Reason i'm asking is because i'm building my menu and i'm implementing security enforced user visibility based on what pages there are in the webbapplication, and what roles each page demands, and display these to the user in the menu.
Using sitemaps are insufficient, i need to provide much more info for all the pages i have on my system.



Using this technique i can query my "PageProvider" for like:
GetAllPagesVisibibleToUser(MembershipUser user)
DoesUserHaveAccessToPage(MembershipUser user, BasePage forPage)
I'm also planning on implementing this technique on WebUserControl ...