Because I'm a massive nerd, I actually try to read specification documents. As I've ranted ad nauseam before, the current TOTP0 spec is irresponsibly obsolete. The three major implementations of the spec - Google, Apple, and Yubico - all subtly disagree on how it should be implemented. Every other MFA app has their own idiosyncratic variants. The official RFC is infuriatingly vague. That's no good

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