Trigger code on user created

[aslakhol]

I should figure out how to trigger some custom code on user created. Perhaps on every login.

Right now I'm thinking it would nice to connect up any attendants with your email when you create an account.

It would also be greeeeeat if I could pass some argument from before the auth flow, perhaps through query params. The problem this could solve is setting a name that is entered before the sign in process somehow.