signingKey := getSigningKey(secretAccessKey, date, region, serviceS3)
	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.

	if redirectURL != nil { // success_action_redirect is valid and set.
		v := redirectURL.Query()
		v.Add("bucket", objInfo.Bucket)
		v.Add("key", objInfo.Name)
		v.Add("etag", "\""+objInfo.ETag+"\"")
		redirectURL.RawQuery = v.Encode()
		writeRedirectSeeOther(w, redirectURL.String())
		return
	}

	// Add checksum header.
	if checksum != nil && checksum.Valid() {
		hash.AddChecksumHeader(w, checksum.AsMap())
	}