code: function CodeRequest(callContext, authenticationContext, clientId, resource) {
      this._log = new Logger('DeviceCodeRequest', callContext._logContext);
      this._callContext = callContext;
      this._authenticationContext = authenticationContext;
      this._resource = resource;
      this._clientId = clientId;
      
      // This should be set at the beginning of getToken
      // functions that have a userId.
      this._userId = null;
  }
docs: Constructs a new CodeRequest object.
  @constructor
  @private
  @param {object} callContext Contains any context information that applies to the request.
  @param {AuthenticationContext} authenticationContext
  @param {string} resource
  @param {string} clientId
   TODO: probably need to modify the parameter list.