[teacup50]

Why on earth would you outsource two factor auth to a cloud service?

Talk about putting all your eggs in the same shared basket.

[markkum]

Funnily; the reason to outsource is exactly about not putting all your eggs in the same shared basket. You outsource the 2nd factor and keep the first factor (passwords) in-house. Implementing everything in-house is a "same shared basket".

[teacup50]

So you're dependent on a cloud startup for basic auth and you've got no more security than any other isolated two factor auth system.