code: function hash(sess) {
    // serialize
    var str = JSON.stringify(sess, function (key, val) {
      // ignore sess.cookie property
      if (this === sess && key === 'cookie') {
        return
      }
  
      return val
    })
  
    // hash
    return crypto
      .createHash('sha1')
      .update(str, 'utf8')
      .digest('hex')
  }
docs: Hash the given `sess` object omitting changes to `.cookie`.
  
  @param {Object} sess
  @return {String}
  @private