code: function(args, cb) {
      var ssn = this.getSessionById(args.sessionId);
      if (!this._authFn) {
        var nodeEnv = process.env.NODE_ENV || "development";
        if (nodeEnv !== "development") {
          var msg = "The Node server you are connecting to appears "
          + "to be a production server, and yet its Vantage.js "
          + "instance does not support any means of authentication. \n"
          + "To connect to this server without authentication, "
          + "ensure its 'NODE_ENV' environmental variable is set "
          + "to 'development' (it is currently '" + nodeEnv + "').";
          ssn.log(chalk.yellow(msg));
          ssn.authenticating = false;
          ssn.authenticated = false;
          cb(msg, false);
        } else {
          ssn.authenticating = false;
          ssn.authenticated = true;
          cb(void 0, true);
        }
      } else {
        this._authFn.call(ssn, args, function(message, authenticated) {
          ssn.authenticating = false;
          ssn.authenticated = authenticated;
          if (authenticated === true) {
            cb(void 0, true);
          } else {
            cb(message);
          }
        });
      }
    }
docs: Calls authentication middleware
  
  @param {Object} args
  @param {Function} cb
  @api private