lazycache2.cs

private static CurrencyExchange GetCurrencyRate(DateTime date)
{
    var key = date.Date.ToString("yyyy-MM-dd");

    return _cache.GetOrAdd(key, () =>
    {
        Console.WriteLine($"{DateTime.UtcNow}: Fetching from service");

        var response = _httpClient.GetAsync("http://api.fixer.io/" + key + "?base=USD").Result;
        var json = response.Content.ReadAsStringAsync().Result;

        return JsonConvert.DeserializeObject<CurrencyExchange>(json);
    }, new TimeSpan(0, 0, 0, 30));
}