Module augmentation

[lokimckay]

Is it possible to include arbitrary fields in the user interface as documented here?
https://authjs.dev/getting-started/typescript#module-augmentation

My attempt:

env.d.ts

declare module "auth-astro" {
  interface User {
    id: string;
    myField: string;
  }
}

auth.config.ts

return defineConfig({
    ...
    callbacks: {
      async jwt({ token, user }) {
        if (user) {
          token.id = user.id;
          token.myField = "foo";
        }
        return token;
      },
      session({ session, token }) {
        session.user.id = token.id as string;
        session.user.myField = token.myField as string; // typescript says: "Property 'myField' does not exist on type 'AdapterUser & User'"
        return session;
      },
    },
  });

Typescript throws the type error:
Property 'myField' does not exist on type 'AdapterUser & User'