[keycloak-dev] Two Factor Authentication via Email.

I'm currently working on a PR that provides "Two factor authentication via email" https://issues.jboss.org/browse/KEYCLOAK-240. My current implementation comes with a custom EmailCodeAuthenticator that generates a short code String in the challenge(...) Method and sends an email to the email address that is configured for the current user. The user can then copy and paste the code into an input field, similar to OTP codes are handled. If the user entered the wrong code, a new email is sent to the user's email address. The email code is saved as a user level credential. I wonder whether this is the right approach or whether it would be better to allow the user to regenerate the code on demand instead of regenerating it every time? For the former I'd have to provide a REST endpoint similar to what happens for verifying an email during registration - where should this be placed? For sending the actual email I'm currently using a EmailSenderProvider, however I think a EmailTemplateProvider might be more appropriate ;-) May I simply add a method to the EmailTemplateProvider interface? Btw. I think this would be a good base for having an SMS based 2nd factor authenticator, as requested here: https://issues.jboss.org/browse/KEYCLOAK-241 It would make sense to have the mobile phone number as a first-class user attribute and showing it on the profile page by default instead of just having it only in the data model. Another point that comes to my mind is that I could make sense to specify an email code policy in the same way OTP policies are supported. This could then be used to differentiate between email codes that are usually handled via copy&paste whereas codes that come via SMS are usually typed in by hand and should therefore be somewhat short ;-) My current WIP can be found here: https://github.com/thomasdarimont/keycloak/commits/issue/KEYCLOAK-240-2nd...