When using a next-auth Provider (Google), How do I use a token generated from my backend API?

[longfellowone]

I found this online (link below). I am trying to insert my own JWT from a custom backend, into the next-auth session. What the example below is showing, is to modify the { user } object in signIn(). This does not work as user is not returned... What is the correct way to accomplish this?

I thought maybe you could do getTokenFromYourAPIServer('github', githubUser) inside the jwt() function. But then how would I reject a user if they were not allowed to sign in?

https://arunoda.me/blog/add-auth-support-to-a-next-js-app-with-a-custom-backend