if err != nil {
		return false
	}
	signature2, err := base64.StdEncoding.DecodeString(sig2)
	if err != nil {
		return false
	}
	return subtle.ConstantTimeCompare(signature1, signature2) == 1
}

// Return canonical headers.
func canonicalizedAmzHeadersV2(headers http.Header) string {
	var keys []string
	keyval := make(map[string]string, len(headers))