[keycloak-user] how to force (kind-of) re-activation when user has logged in from a new location ?

[The Fredo]

Hi all,
I'd like :   
   - to detect that a user has just logged in from a new "location" (e.g. userAgent, IP, etc..).
   - If such event happens, I'd like to make him perform a new account activation, like he did when he registered, i.e. send an activation email.

I read in the doc that Keycloak is open and offers the possibility to add custom behavior through plugins.But I don't know where to start exactly ie.   
   - how/where to intercept the login flow to add by own code (i.e. just after the successful authentication)
   - how to trigger this kind of new activation (probably by adding a required action, but how exactly?)

Any leads would be appreciated since I'm discovering Keycloak.
I'm currently using KC 2.5.4  + (KC proxy) but no problem to upgrade if necessary.
Thanks !