code: function(app, opts) {
    opts = opts || {};
    this.app = app;
    this.service = new SessionService(opts);
  
    let getFun = function(m) {
      return (function() {
            return function() {
              return self.service[m].apply(self.service, arguments);
            };
      })();
    };
    // proxy the service methods except the lifecycle interfaces of component
    let method, self = this;
    for(let m in this.service) {
      if(m !== 'start' && m !== 'stop') {
        method = this.service[m];
        if(typeof method === 'function') {
          this[m] = getFun(m);
        }
      }
    }
  }
docs: Session component. Manage sessions.
  
  @param {Object} app  current application context
  @param {Object} opts attach parameters