This is a solved problem surely?
Thanks to two factor authentication my bank knows exactly who I am. Thanks to the wonders of encryption I can be fairly sure that no prying eyes can read the contents of my transmissions.
If banks can do this kind of thing for online banking then why can't the government? It's not even hard! I think even Blizzard use a similar system for protecting it's users too. If it can be done for video games, it can be done for the DWP.