code: def credentials(self):
          
          if self._credentials is None:
              self._credentials, _ = google.auth.default()
          return self._credentials
docs: google.auth.credentials.Credentials: Credentials to use for queries
          performed through IPython magics
  
          Note:
              These credentials do not need to be explicitly defined if you are
              using Application Default Credentials. If you are not using
              Application Default Credentials, manually construct a
              :class:`google.auth.credentials.Credentials` object and set it as
              the context credentials as demonstrated in the example below. See
              `auth docs`_ for more information on obtaining credentials.
  
          Example:
              Manually setting the context credentials:
  
              >>> from google.cloud.bigquery import magics
              >>> from google.oauth2 import service_account
              >>> credentials = (service_account
              ...     .Credentials.from_service_account_file(
              ...         '/path/to/key.json'))
              >>> magics.context.credentials = credentials
  
  
          .. _auth docs: http://google-auth.readthedocs.io
              /en/latest/user-guide.html#obtaining-credentials