code: func (rt *registryRoundTripper) NewRequest(method, path string,
  	query *url.Values, body interface{}) (*http.Request, error) {
  
  	req, err := rt.DefaultRequestDoer.NewRequest(method, path, query, body)
  
  	if err != nil {
  		return nil, err
  	}
  
  	if rt.holder.HasToken() {
  		req.Header.Set("Authorization", "Bearer "+string(rt.holder.Token()))
  	}
  
  	req.Header.Set("User-Agent", "Torus-Daemon/"+rt.version)
  	req.Header.Set("X-Registry-Version", rt.apiVersion)
  
  	return req, nil
  }
docs: // Augment the default NewRequest to set additional required headers