Integration with custom backend using passport

[oddnugget]

Greetings! I am trying to wrap my head around how to integrate NextAuth with a custom backend written in nest.js. I understand how i can make use of the various callbacks that exist in NextAuth to validate the user with my backend, the part i have trouble with is that since NextAuth already does the OAuth flow, i need to just replace the backchannel part with that of my backend. I'm using passport on the backend, and the strategies i have tried all seem to expect the flow to be initialized from that domain. Ideally i would like to just pass the access token and verify that, but it seems to be impossible.

The other option would be to somehow tell NextAuth to use my backend for the frontchannel parts as well, but this seems needlessly complicated.

Anyone had a similar problem or has any tips?