code: func DiscoveryToken() string {
  	if len(modes) == 0 {
  		return Token()
  	}
  	if _, ok := modes[0].(None); ok {
  		return OmitAuthToken
  	}
  	return Token()
  }
docs: // DiscoveryToken returns OmitAuthToken if the first registered auth mode is of
  // type None, and Token() otherwise.