function getHeaderValueToSign(request, headerName) {
        const value = request.headers.get(headerName);
        if (!value) {
            return "";
        }
        // When using version 2015-02-21 or later, if Content-Length is zero, then
        // set the Content-Length part of the StringToSign to an empty string.
        // https://learn.microsoft.com/en-us/rest/api/storageservices/authenticate-with-shared-key
        if (headerName === HeaderConstants.CONTENT_LENGTH && value === "0") {
            return "";
        }
        return value;
    }
Retrieve header value according to shared key sign rules.
@see https://learn.microsoft.com/en-us/rest/api/storageservices/authenticate-with-shared-key