code: func (im *imp) doCredAPI(ctx context.Context, clientID, clientSecret string, result interface{}, apiPath string, keyval ...string) error {
  	form := url.Values{}
  	form.Set("client_id", clientID)
  	form.Set("client_secret", clientSecret)
  	return im.doAPI(ctx, form, result, apiPath, keyval...)
  }
docs: // doCredAPI makes userless requests to the Foursquare API, which have a larger
  // quota than user requests for some endpoints.
  // https://developer.foursquare.com/overview/auth#userless
  // https://developer.foursquare.com/overview/ratelimits