class Google::Auth::ServiceAccountCredentials

def enable_self_signed_jwt?
  # Use a self-singed JWT if there's no information that can be used to
  # obtain an OAuth token, OR if there are scopes but also an assertion
  # that they are default scopes that shouldn't be used to fetch a token,
  # OR we are not in the default universe and thus OAuth isn't supported.
  target_audience.nil? && (scope.nil? || @enable_self_signed_jwt || universe_domain != "googleapis.com")
end