code: function (protocol, host, port, username, password, onConnected) {
      this.rocketChatClient = new RocketChatClient(protocol, host, port, username, password, onConnected);
      this.token = null;
  
      /**
       * login the rocket chat
       * @param callback after login the rocket chat , will invoke the callback function
       */
      this.login = function (username, password, callback) {
          var self = this;
          this.rocketChatClient.authentication.login(username, password, function (err, body) {
              
              self.token = body.data;
              callback(null, body);
          });
      };
  }
docs: Rocket Chat Api constructor
  @param protocol rocket chat protocol
  @param host rocket chat host , default is https://demo.rocket.chat
  @param port rocket chat port , default is 80
  @param username rocket chat username
  @param password rocket chat password
  @param onConnected callback that is invoked when connection is open
  @constructor