header
containers/image is the dominant client library to interact with
registries.
It detects which authentication to use based on the WWW-Authenticate
header returned when pinging "/v2/" end-point. If we didn't return this
header, then creds are not used for other write-protected end-points.
Hence, the compatibility fix.
New options added to configuration file to reference a public key used
to validate authorization tokens signed by an auth server with
corresponding private key.
Resolves#24
Signed-off-by: Peter Engelbert <pmengelbert@gmail.com>