two factor authentication for weblogin

[elkas88]

Is your feature request related to a problem? Please describe.
No, but security related. For a public facing application it would be nice to have the possibility to activate 2FA for users.

Describe the solution you'd like
A solution to be able to use the Google Authenticator, Microsoft Authenticator or any similar app which can scan a QR code and generate a time based code for the second factor.

Additional context
Another slider button in the "Edit user" dialog "enable 2fa" which when it's turned on generates the QR code and shows them between the button and the save button.

[jmattheis]

Yes, sounds like a good feature, but I think it rather should be outsourced via an external auth service #433, this way this doesn't have to be implemented inside gotify.