code: func (rt *apiRoundTripper) newRequest(method, prefix, path string,
  	query *url.Values, body interface{}) (*http.Request, string, error) {
  
  	requestID := uuid.NewV4().String()
  
  	prefixed := "/" + prefix + path
  	req, err := rt.DefaultRequestDoer.NewRequest(method, prefixed, query, body)
  	if err != nil {
  		return nil, requestID, err
  	}
  
  	req.Header.Set("X-Request-ID", requestID)
  
  	return req, requestID, nil
  }
docs: // newRequest augments the default to set a unique request id