How to connect a new sign-up to an existing database record?

Is it possible to send a custom data field to Auth0 that is returned on the /callback after sign-up? Or in other words, is there a way to connect a new Auth0 user to an existing record in my Application?

I have an Application scenario where a Player can sign up for an online game in person. They are given an “Activation Code” that connects them with a Team/Game in my database that I have prepped. I’d like them to enter the 8-digit code, then Click “Activate”, that routes them to Auth0 to create an ID and a Password. They’re then routed back to my Application and I’d like that 8 digit code to be sent with the /callback so that I can connect that login with the Player in my database.

As an alternative, maybe it’s possible to save that 8-digit activation code within my Node JS layer before calling Auth0, but I don’t think that data would be connectable to the Auth0 callback.

Thanks!
Jon

It looks like I may have found a workaround solution for this… I may be able to use the State parameter to add the 8-digit ID to my initial Auth0 sign-up request. When the callback response returns I can check the State parameter returned and connect that call to the original requestor. Link below. Does this seem reasonable?