Sharing session with iframe parent (angularjs)

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I have what I expect (and hope) to be a fairly rare use case. I am working on a nextjs app which has to integrate with a preexisting angular.js app, which is being phased out. The angular app is the landing page, and currently next modules are embedded as iframes, as we migrate components. So far, the integrated modules have not needed authentication, so the problem has not yet been solved.

Keycloak is being used as an auth provider, and currently the sessions are managed manually. I would ideally like to transition to using next-auth. Is there any way I could configure next-auth such that it can check for a cookie (which my angular app would provide) which contians enough credentials to create a next-auth session behind the scenes, without the user needing to log in again?

If not, is the configuration of the session token documented anywhere? If I could recreate that in my angular app, I believe that should solve my problem, as then when my next app loads within the iframe, it would find the session token cookie, and go from there.