getvalueToAppend = function (value, headerName) {
    // Do not sign content-length 0 in 2014-08-16 and later
    if (headerName === HeaderConstants.CONTENT_LENGTH && (azureutil.objectIsNull(value[headerName]) || value[headerName].toString() === '0')) {
      return '\n';
    } else if (azureutil.objectIsNull(value) || azureutil.objectIsNull(value[headerName])) {
      return '\n';
    } else {
      return value[headerName] + '\n';
    }
  }
Signs a request with the Authentication header.

@param {WebResource}      webResource The webresource to be signed.
@param {function(error)}  callback    The callback function.