How to restrict a page to a group of people? I am trying to figure out how I can lock down a page (part of my site) to a list of users that I have in another MySQL DB.

Ideally I would like to call the DB and see if the user has access each time they login. Is there any modules that would do this? Or has anyone done anything similar before.
You can add the secondary database to Drupal by following this tutorial: https://www.drupal.org/node/18429

I would probably run a hook_node_view so that it's called before rendering the node and adding your custom logic there.