'next-auth' with google question

Hello my dear developer!

I'm calling for your help. This topic is new to me, please be a bit lenient with me. Also it's my first post on Reddit! Getting grilled would ruin my day. Thank you very much :-)

I’m using 'next-auth' to let users sign up with google. This works. I get the user and account data back from google inside the signIn callback in the [...nextauth].ts file. With this information I create a user profile on my backend service.

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Snippet 1: perfectly working signIn callback with next-auth

However I have two different types of users: athletes and organisers. They use separate forms to sign up on the same website. I would like to let both athletes and organisers sign up with google. But how do I get this information to the signIn callback from "Snipped 1"?

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My approach was to pass this information through the authorizationParams in the signIn method.

Snippet 2: Button that passes the userType as authorizationParams

This now brings me the userType at least to the URL as a parameter in the oauth consent screen . But if I select an account now: How I can work with this userType now in my signIn callback? How do I get this parameter back to my application?

Snipped 3: Google oauth consent

Any help would be so much appreciated. I googled the half web for an answer and couldn't find an answer. Maybe I'm searching for the wrong things. I'm lost. Help me. Please :D