func generateCredentialStr(accessKey, date, region, service, requestVersion string) string {
	return "Credential=" + joinWithSlash(accessKey, date, region, service, requestVersion)
}

// joins the argument strings with a '/' and returns it.
func joinWithSlash(accessKey, date, region, service, requestVersion string) string {
	return strings.Join([]string{
		accessKey,
		date,
		region,
		service,