Ldap – How to implement successive LDAP authentications on an Apache site

I have a small Apache site which I've successfully implemented basic LDAP authentication using mod_authz_ldap. However, I am having a problem trying to implement two levels of successive authentication. Once a valid user is authenticated once, they are never prompted for secondary authentication which should be required for a specific part of the site. That is, all valid users can login, but they are never re-authenticated when only a subset of those users should access parts of the site.

For example, I required everyone who visits example.com to be authenticated as a valid LDAP user. Then I have a subversion repository at example.com/websvn which I want to restrict to only the 'development' group, a subset of the valid users.

My problem is that once a user is successfully authenticated as valid at example.com, when they navigate to example.com/websvn they are never re-prompted for authentication as a 'development' user. This happens even when the valid user is indeed not in the development group. I can test the repo authentication by freshly connecting directly to example.com/websvn, but when I first authenticate at example.com, and then visit example.com/websvn I am granted access no matter what, and never prompted for a password.

How do I properly implement a two-stage authentication like this? I want all valid users to access the main site, but only development users to have access to websvn. So valid users must be re-authenticated to check if they are in the development group.

Thanks!