Base64DateTimeHelpers.cs

public static class Base64DateTimeHelpers
{
	public static string ToBase64(this DateTimeOffset dateTimeOffset)
	{
		var seconds = dateTimeOffset.ToUnixTimeSeconds();
		var buffer = BitConverter.GetBytes(seconds);
		return Convert.ToBase64String(buffer);
	}

	public static string ToBase64UrlSafe(this DateTimeOffset dateTimeOffset)
	{
		return dateTimeOffset.ToBase64().Replace('+', '-').Replace('/', '_').TrimEnd('=');
	}
}