// b64replace +,/,-,_ with A and Z
func b64replace(s string) string {
	s = strings.Replace(s, "+", "A", -1)
	s = strings.Replace(s, "-", "A", -1)
	s = strings.Replace(s, "/", "Z", -1)
	s = strings.Replace(s, "_", "Z", -1)
	return s
}