AuthenticateResponse add authentication headers on request.

DownloadManifest the manifest for the given image, using the given credentials.

DownloadV1Manifest the manifest for the given image in v1 schema format, using the given credentials.

GetAuthCredentials returns the auth credentials (if any found) for the given repository, as found in the user's docker config.

ErrUnauthorized is return when requested user don't have access to the resource.