Two-factor authentication without trusted devices?

Well that was fun... Not!

I had to create a new user account on my Mac, and sign into iCloud on that account using the Enterprise Developer account in order just to enable two-factor authentication on that Apple ID.

Then, I had to sign out of that account, sign into my primary user account on my Mac, go to System Preferences | Internet Accounts | iCloud and add a new iCloud account -- the Enterprise Developer account. But don't forget to turn OFF synchronization of the contacts, and calendars and such, or else all your personal contacts get uploaded to the Enterprise Developer account! Do it quickly!

But *finally* the stupid thing will let me sign into my developer account. Ridiculous. What the **** was wrong with two-step authentication where you receive a text on a trusted phone?

They do NOT make it obvious that you can even USE two-factor authentication on an account that doesn't actually own any devices -- they need to make that a much more prevalent thing in the FAQ. But it's finally done...