code: func (otp *HOTP) URL(label string) string {
  	secret := base32.StdEncoding.EncodeToString(otp.Key)
  	u := url.URL{}
  	v := url.Values{}
  	u.Scheme = "otpauth"
  	u.Host = "hotp"
  	u.Path = label
  	v.Add("secret", secret)
  	v.Add("counter", fmt.Sprintf("%d", otp.Counter()))
  	u.RawQuery = v.Encode()
  	return u.String()
  }
docs: // URL returns a suitable URL, such as for the Google Authenticator
  // app. The label is used by these apps to identify the service to
  // which this OTP belongs. The digits value is ignored by the Google
  // authenticator app, and is therefore elided in the resulting URL.