code: func makeRedirectURL(base, dest string) (string, error) {
  	dest, err := normalizeURL(dest)
  	if err != nil {
  		return "", err
  	}
  	v := url.Values{}
  	v.Set("r", dest)
  	return base + "?" + v.Encode(), nil
  }
docs: // makeRedirectURL is used to generate login and logout URLs.