How to keep $request data after authentication?

I am building an app which allows a user to fill in the form, choose files for upload without authentication. When a user clicks submit he, actually, posts data to a route protected by auth. The problem is that if the user was not logged in before the POST, the $request data is lost after entering the credentials. So, it should work like this: User submits data ->If user is not logged in->User logs in->User gets to a protected rout with the POSTed $request data.

How to achieve this? What would be the best approach?

Thanks!

via Chebli Mohamed