Option to make 2FA mandatory

[Moc]

The option to make 2FA mandatory, required during signup. (and no option to turn it off, only add a new account). ie. no 2fa, no login, period.

Perhaps also filter on userclass so, for example, the main admin could obligate all admins to use 2FA.

(Thanks @CaMer0n)

[Moc]

@CaMer0n In order to do this I need some guidance. This plugin uses an e_user.php file to create a new EUF. It displays a text link (enable/disable) in the usersettings page.

I need some way to add a check somewhere whether or not the EUF (secret_key) has been filled or not, to determine whether or not 2FA has already been enabled, and then a way to force the user to enable it. The check if it's enabled is easy, but how do I force a user to enable it?

In case of a textbox or dropdown EUF it's easily done, but how to do it in this case with a text link?