TimeZoneService.cs

public class TimeZoneService : ITimeZoneService
{
    private const string ContainerName = "azfnv2demo";
    private const string FileName = "timezones.json";

    private readonly IAzureBlobStorageHelper _azureBlobStorageHelper;

    public TimeZoneService(IAzureBlobStorageHelper azureBlobStorageHelper)
    {
        _azureBlobStorageHelper = azureBlobStorageHelper;;
    }

    public async Task<IEnumerable<string>> GetTimeZones()
    {
        var jsonContent = await _azureBlobStorageHelper.DownloadBlobContent(ContainerName, FileName).ConfigureAwait(false);
        return string.IsNullOrEmpty(jsonContent) ? null : JsonConvert.DeserializeObject<IEnumerable<string>>(jsonContent);
    }
}