/// <summary>
/// Saves persistent keys to a file asynchronously. The server does this automatically.
/// </summary>
/// <param name="filename">The file name.</param>
/// <exception cref="PersistentException">Thrown if there is an error
/// saving the file.</exception>
public static async Task <string> SavePersistentAsync(string filename)
{
return(await NtCore.SavePersistentAsync(filename).ConfigureAwait(false));
}