The List Docker Repositories API lets you list images available in a repo. However, when this API is used against a remote repository (or a virtual with a remote aggregated within), you may see the below error.
“Unable to fetch catalog from 'https://registry-1.docker.io/v2/_catalog?': HTTP/1.1 401 Unauthorized”
This is due to the remote repository upstream site not supporting the _catalog API, and is usually not an issue, but the error may be misleading.