usability testing – How do you prototype systems that are normally connected to Active Directory or other complex external systems?

I am working on a product that has a quite typical setup when it comes to enterprise software: it is usually connected to the Active Directory of the origanization and authenticates its users against it and fetches their group membership information from it. The permissions within the products are assigned to the groups that come from AD. For tiny installations and in test scenarios it is possible to add local users and groups but in production usage it is almost always integrated with Active Directory.

We are planning on making some pretty significant changes in how permission settings can be made and the mockups for the changes tested well when local users & groups were used. We would now like to see if the interface works well in a more realistic scenario when the product is connected to AD and we have thousands of users and groups.

I was wondering on whether you have any experience or insight on how to do users tests in such a situation. Creating and maintaining a fake, internet-facing AD installation seems to be an overkill for this purpose and also cause problems during the test as well as it’d be impossible to connect the real AD with the wireframe we want to test. Creating a mock AD user management interface would also take tons of time and would probably still be quite far from how that UI works normally.

Do you have any experience with this or more generally speaking on doing wireframe tests of systems that are normally connected to large, complex external systems in production?