var cache = new CachingService
            {
                DefaultCachePolicy = {DefaultCacheDurationSeconds = 1}
            };

            var res1 = await cache.GetOrAddAsync("foo", async x => DateTime.UtcNow.Second);

            // wait for the item to expire
            await Task.Delay(TimeSpan.FromSeconds(2));

            // same key
            var res2 = await cache.GetOrAddAsync("foo", async x => DateTime.UtcNow.Second);
            // new key
            var res3 = await cache.GetOrAddAsync("bar", async x => DateTime.UtcNow.Second);
            
            Console.WriteLine(res1);
            Console.WriteLine(res2);
            Console.WriteLine(res3);

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