In one embodiment, a validation server in a computer network determines that an edge router of the computer network has blocked access to a desired server address based on the edge router not having authentication information for the desired server address. In response, the server creates a white-listing policy to temporarily allow access to the desired server address at the edge router, and sends the white-listing policy to the edge router. The validation server may then proceed with performing server fetching operations to the desired server address from the validation server while the white-listing policy is in effect, and instructs the edge device to remove the white-listing policy once the server fetching operations are completed.