code: function expireSessionIDs(){
      var tssec = Date.now();
      var expired = [];
      for(var sid in sessionIDs){
          if(sessionIDs[sid] < (tssec + 500)){
              expired.push(sid);
          }
      }
      for(var i=0;i<expired.length;i++){
          delete sessionIDs[expired[i]];
          debug('Session ID expired: %s', expired[i]);
      }
  }
docs: If authentication is enabled, executed periodically and expires old session IDs