Dynamic Output by Category or Tag?

Is there any way to have the sitemap dynamically display only the pages and posts that either have a specific category or tag? Our site has all of the regular pages intended for the public, which should always be on the sitemap, but also a number of pages that are meant to be seen by invitation only (password protected or otherwise), and I don’t want those on the sitemap. But there are lots of them, and they change all the time, so I don’t want to have to keep updating the “excluded” post id’s on my sitemap shortcode.