code: function requireValidCacheClient (cacheClient) {
      // require object for cache client
      if (!cacheClient || typeof cacheClient !== 'object') {
          throw new Error('cacheClient error: cacheClient must be object')
      }
      // check for all required methods
      _.each(requireMethods, method => {
          if (typeof cacheClient[method] !== 'function') {
              throw new Error ('cacheClient error: cacheClient must provied '+method+' method')
          }
      })
  }
docs: @function requireValidCacheClient
  
  throw error if cacheClient object does not expose methods:
  - get(key, session)
  - set(key, value, session)
  - setex(key, value, exp, session)
  
  @param {object} cacheClient
  
  @returns {undefined}
  
  @throws {Error} on invalid name