jsctl registry auth output --format=dockerconfig produces a JSON object with four attributes: username, password, email and auth. Both password and auth are derived from the contents of ~/.jsctl/eu.gcr.io--jetstack-secure-enterprise.json making the resultant JSON look more complicated than it actually is. That would be fine if this complexity served an identifiable purpose.
Given that auth and password are equivalent, I suspected that one was not strictly needed to gain access to the private registry. This suspicion appears to be correct and the password attribute is indeed surplus to requirements.
You can (IMO should) remove the password attribute from the result of jsctl registry auth output --format=dockerconfig.