From the 'Users' section click on any of the names in the list. For this example, we are going to pick on Joe Blow, who we do not trust.

Click 'Edit access list'

By default Joe Blow has access to all cameras. We do not want him to have access to cameras, simply click on the camera name. This will change the color of the camera from green (full access) to red (no access). Joe Blow will not see the camera in the available video devices, or in the event / search area. Changes are applied instantly.