code: func TransportFor(config *Config) (http.RoundTripper, error) {
  	cfg, err := config.TransportConfig()
  	if err != nil {
  		return nil, err
  	}
  	return transport.New(cfg)
  }
docs: // TransportFor returns an http.RoundTripper that will provide the authentication
  // or transport level security defined by the provided Config. Will return the
  // default http.DefaultTransport if no special case behavior is needed.