public class MemoryCacheTicketStore : ITicketStore
        {
            private const string KeyPrefix = "AuthSessionStore-";
            private readonly IMemoryCache _cache;

            public MemoryCacheTicketStore()
            {
                _cache = new MemoryCache(new MemoryCacheOptions());
            }

            public async Task<string> StoreAsync(AuthenticationTicket ticket)
            {
                var guid = Guid.NewGuid();
                var key = KeyPrefix + guid.ToString();
                await RenewAsync(key, ticket);
                return key;
            }

            public Task RenewAsync(string key, AuthenticationTicket ticket)
            {
                var options = new MemoryCacheEntryOptions();
                var expiresUtc = ticket.Properties.ExpiresUtc;
                if (expiresUtc.HasValue)
                {
                    options.SetAbsoluteExpiration(expiresUtc.Value);
                }
                options.SetSlidingExpiration(TimeSpan.FromHours(1)); // TODO: configurable.

                _cache.Set(key, ticket, options);

                return Task.FromResult(0);
            }

            public Task<AuthenticationTicket> RetrieveAsync(string key)
            {
                AuthenticationTicket ticket;
                _cache.TryGetValue(key, out ticket);
                return Task.FromResult(ticket);
            }

            public Task RemoveAsync(string key)
            {
                _cache.Remove(key);
                return Task.FromResult(0);
            }
        }