// 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);
        }