'docker-content-digest' header is not returned with requests for a tag
Crane and Pulp don't set the 'Docker-content-digest' header . Users want to make a HEAD request for a tag to find out if that tag is pointing to a new manifest. Without this header, users must download the manifest in order to learn its digest.
The first thing that I found when searching the web is a bug about Crane. We need to fix this for Pulp 3.