Add a one time password code for admins

[Falco]

Duplicate of

Two-factor local login option

So, authentication on Discourse seems like mostly a solved problem since you can offload it to an external provider, but I’d love for Discourse to have a two-factor option for local authentication. It seems relatively uncomplicated to bolt-on support for TOTP via Google Authenticator—for example, here’s a Google Authenticator add-on implementation in PHP for Roundcube. Right, right, apples and oranges, php and ruby, webmail and forum, but the libraries are all there and it’d definitely make me h…