code: function set_session(req,cb){
  
      // ttl stuff borrowed & modified from  visionmedia / connect-redis.js  source code
      // Copyright(c) 2012 TJ Holowaychuk <tj@vision-media.ca>  MIT Licensed
  
      try {
          var maxAge = req.session.cookie.maxAge
          var ttl = _ttl || ('number' == typeof maxAge
                            ? maxAge / 1000 | 0
                            : oneDay)
          redclient.setex(req.session.st, ttl, req.sessionID, function(err){
              if(!err){
                   logger.debug('SETEX session ticket, max age ' + ttl);
              }
              cb && cb(err)
          })
      } catch (err) {
          logger.error('saving session ticket to Redis threw an error')
          //throw new Error(err)
          cb && cb(err);
      }
  }
docs: set_session
  
  store the session id, and the CAS session ticket in Redis, for
  single sign off.
  
  uses the 'req' object to pull out the st and sessionid, and also to
  determine the maxage set for the session