JsonAppConfigService.cs

using Microsoft.Extensions.Configuration;

namespace CoolApp.ApplicationService
{
    public class JsonAppConfigService : IAppConfigService 
    {
        private readonly string _defaultCurrency;
        public JsonAppConfigService(IConfiguration configuration)
        {
            _defaultCurrency = configuration["DefaultCurrency"];
        }

        public string GetDefaultCurrency() => _defaultCurrency;
    }
}