// Get canonical URI.
	canonicalURI := s3utils.EncodePath(req.URL.Path)

	// Get canonical request.
	// canonicalRequest =
	//  <HTTPMethod>\n
	//  <CanonicalURI>\n
	//  <CanonicalQueryString>\n
	//  <CanonicalHeaders>\n
	//  <SignedHeaders>\n
	//  <HashedPayload>
	//
	canonicalRequest := strings.Join([]string{
		req.Method,
		canonicalURI,
		req.URL.RawQuery,
		canonicalHeaders,