Decode ASPXAUTH FormsAuthentication Cookie

Small Windows Forms utility for quickly decoding an ASPXAUTH Cookie that has been set using FormsAuthentication. You must provide the MachineKey's ValidationKey and DecryptionKey field values.

Thanks to @david-mitchell for the groundwork in his gist at: https://gist.github.com/david-mitchell/5350992

Free to reuse as you see fit. No attribution necessary.