func parseSignature(signElement string) (string, APIErrorCode) {
	signFields := strings.Split(strings.TrimSpace(signElement), "=")
	if len(signFields) != 2 {
		return "", ErrMissingFields
	}
	if signFields[0] != "Signature" {
		return "", ErrMissingSignTag
	}
	if signFields[1] == "" {
		return "", ErrMissingFields
	}
	signature := signFields[1]
	return signature, ErrNone
}