GetCurrentRate.cs

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

    var cachedExchange = _cache.GetAsync<CurrencyExchange>(key).Result;

    if (cachedExchange.HasValue)
    {
        Console.WriteLine("Found in cache");
        return cachedExchange.Value;
    }

    Console.WriteLine("Fetching from service");

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

    var exchange = JsonConvert.DeserializeObject<CurrencyExchange>(json);
    _cache.AddAsync(key, exchange).Wait();
    
    return exchange;
}