We are using a Closed User Group to protect an area of our website. We have though discovered an issue that a user can copy a link to a DAM document under the secure area, logout and they are still able to access the DAM document but pasting the copied URL in to the address bar.
Is there a way to protect the DAM assets as well as the page content.
Does the assets are shown as protect at http://<host>:<port>/system/console/cug ?
If not IIRC there is no ui either you need to customize dam asset editor by overlaying OR make sure the properties  are set properly for the assets.
Courtesy to Justin Edelson.
Enabled - cq:cugEnabled
Login Page - cq:cugLoginPage
Principals - cq:cugPrincipals
Realm - cq:cugRealm
Europe, Middle East and Africa