code: func base64Decode(s string) ([]byte, error) {
  	// add back missing padding
  	switch len(s) % 4 {
  	case 2:
  		s += "=="
  	case 3:
  		s += "="
  	}
  	return base64.URLEncoding.DecodeString(s)
  }
docs: // base64Decode decodes the Base64url encoded string