code: def unpack_auth_b64(self, docker_registry):
          
          UnpackedAuth = namedtuple('UnpackedAuth', ['raw_str', 'username', 'password'])
          credentials = self.get_credentials(docker_registry)
          auth_b64 = credentials.get('auth')
          if auth_b64:
              raw_str = b64decode(auth_b64).decode('utf-8')
              unpacked_credentials = raw_str.split(':', 1)
              if len(unpacked_credentials) == 2:
                  return UnpackedAuth(raw_str, *unpacked_credentials)
              else:
                  raise ValueError("Failed to parse 'auth' in '%s'" % self.json_secret_path)
docs: Decode and unpack base64 'auth' credentials from config file.
  
          :param docker_registry: str, registry reference in config file
  
          :return: namedtuple, UnpackedAuth (or None if no 'auth' is available)