The authentication for it was simple and reasonably secure: they physically mailed me a card with a verification number I had to type in. It took a few days of course, but only someone with access to my mailbox can get the card (and my mailbox requires a key to open).
This "knowledge-based authentication" system USPS is using is most definitely less secure, and I can't fathom how it wouldn't be immensely more complex to build and maintain.