Marking users as new when created via a backend's authenticate in Django

Question

I have an authentication backend based off a legacy database. When someone logs in using that database and there isn't a corresponding User record, I create one. What I'm wondering is if there is some way to alert the Django system to this fact, so that for example I can redirect the brand-new user to a different page.

The only thing I can think of is adding a flag to the users' profile record called something like is_new which is tested once and then set to False as soon as they're redirected.

Basically, I'm wondering if someone else has figured this out so I don't have to reinvent the wheel.