func isReqAuthenticated(ctx context.Context, r *http.Request, region string, stype serviceType) (s3Error APIErrorCode) {
	if errCode := reqSignatureV4Verify(r, region, stype); errCode != ErrNone {
		return errCode
	}

	clientETag, err := etag.FromContentMD5(r.Header)
	if err != nil {
		return ErrInvalidDigest
	}

	// Extract either 'X-Amz-Content-Sha256' header or 'X-Amz-Content-Sha256' query parameter (if V4 presigned)

	}

	// X-Amz-Copy-Source shouldn't be set for this call.
	if _, ok := r.Header[xhttp.AmzCopySource]; ok {
		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidCopySource), r.URL)
		return
	}

	clientETag, err := etag.FromContentMD5(r.Header)
	if err != nil {
		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidDigest), r.URL)
		return
	}

	// if Content-Length is unknown/missing, throw away