signature := getSignature(signingKey, stringToSign)

	req.URL.RawQuery = query.Encode()

	// Add signature header to RawQuery.
	req.URL.RawQuery += "&X-Amz-Signature=" + url.QueryEscape(signature)

	// Construct the final presigned URL.
	return nil
}

// preSignV2 - presign the request in following style.