code: func (t *cachedTokenSource) baseCache() map[string]string {
  	t.lk.Lock()
  	defer t.lk.Unlock()
  	ret := map[string]string{}
  	for k, v := range t.cache {
  		ret[k] = v
  	}
  	delete(ret, "access-token")
  	delete(ret, "expiry")
  	return ret
  }
docs: // baseCache is the base configuration value for this TokenSource, without any cached ephemeral tokens.