public TokenDbCache(string userObjectId)
        {
           // associate the cache to the current user of the web app
            userObjId = userObjectId;
            
            this.AfterAccess = AfterAccessNotification;
            this.BeforeAccess = BeforeAccessNotification;
            this.BeforeWrite = BeforeWriteNotification;

            // look up the entry in the DB
            Cache = db.TokenCacheEntries.FirstOrDefault(c => c.userObjId == userObjId);
            // place the entry in memory
            this.Deserialize((Cache == null) ? null : Cache.cacheBits);
        }
 // 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.TokenCacheEntries.FirstOrDefault(c => c.userObjId == userObjId);
     }
     else
     {   // retrieve last write from the DB
         var status = from e in db.TokenCacheEntries
                      where (e.userObjId == userObjId)
                      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.TokenCacheEntries.FirstOrDefault(c => c.userObjId == userObjId);
         }
     }
     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 TokenCacheEntry
         {
             userObjId = userObjId,
             cacheBits = this.Serialize(),
             LastWrite = DateTime.Now
         };
         //// update the DB and the lastwrite                
         db.Entry(Cache).State = Cache.TokenCacheEntryID == 0 ? EntityState.Added : EntityState.Modified;                
         db.SaveChanges();
         this.HasStateChanged = false;
     }
 }