// constructor
    public EFADALTokenCache(string user) {
      // associate the cache to the current user of the web app
      User = user;

      this.AfterAccess = AfterAccessNotification;
      this.BeforeAccess = BeforeAccessNotification;
      this.BeforeWrite = BeforeWriteNotification;

      // look up the entry in the DB
      Cache = db.PerUserCacheList.FirstOrDefault(c => c.webUserUniqueId == User);
      // place the entry in memory
      this.Deserialize((Cache == null) ? null : Cache.cacheBits);
    }
 // Notification raised after ADAL accessed the cache.
 // If the HasStateChanged flag is set, ADAL changed the content of the cache
 void AfterAccessNotification(TokenCacheNotificationArgs args) {
   // if state changed
   if (this.HasStateChanged) {
     Cache = new PerWebUserCache {
       webUserUniqueId = User,
       cacheBits = this.Serialize(),
       LastWrite = DateTime.Now
     };
     //// update the DB and the lastwrite                
     db.Entry(Cache).State = Cache.EntryId == 0 ? EntityState.Added : EntityState.Modified;
     db.SaveChanges();
     this.HasStateChanged = false;
   }
 }
    // Notification raised before ADAL accesses the cache.
    // This is your chance to update the in-memory copy from the DB, if the in-memory version is stale
    void BeforeAccessNotification(TokenCacheNotificationArgs args) {
      if (Cache == null) {
        // first time access
        Cache = db.PerUserCacheList.FirstOrDefault(c => c.webUserUniqueId == User);
      } else {   // retrieve last write from the DB
        var status = from e in db.PerUserCacheList
                     where (e.webUserUniqueId == User)
                     select new {
                       LastWrite = e.LastWrite
                     };
        // if the in-memory copy is older than the persistent copy
        if (status.First().LastWrite > Cache.LastWrite)
        //// read from from storage, update in-memory copy 
        {
          Cache = db.PerUserCacheList.FirstOrDefault(c => c.webUserUniqueId == User);
        }
      }


      this.Deserialize((Cache == null) ? null : Cache.cacheBits);
    }