nextauth 4x credentials sign in – how to append additional db data to user session

I am trying to build a simple credentials sign flow using next-auth ^4.24.5 with nextjs 14. My user model has a boolean prop called ‘isAdmin’ that I would like to expose out to my session using a jwt strategy.

I can see the isAdmin prop as part of the returned user from User.find().
However, I do not see it as part of ANY object returned from any of the callbacks.

This is my config:

import NextAuth from "next-auth";
import CredentialsProvider from "next-auth/providers/credentials";
import User from "../../../../models/User";

export const authOptions = {
  secret: process.env.NEXTAUTH_SECRET,
  session: {
    strategy: "jwt"
  },
  providers: [
    CredentialsProvider({
      name: "Credentials",

      credentials: {
        username: {
          label: "Username",
          type: "text",
          placeholder: "[email protected]",
        },
        password: { label: "Password", type: "password" },
      },
      async authorize(credentials, req) {
        try {
          const user = await User.findOne({
            email: credentials.username,
          }).exec();
          if (user) {
            const isValid = await user.comparePassword(credentials.password);
            if (isValid) return user;
          }

          return null;
        } catch (err) {
          console.log(err);
        }
      },
    }),
  ],
  callbacks: {
    async signIn({ user, account, profile, email, credentials }) {
      return true;
    },
    async redirect({ url, baseUrl }) {
      return baseUrl;
    },
    async jwt({ token, user, account, profile, isNewUser }) {
      return token;
    },
    async session({ session, user, token }) {
      return session;
    },
  },
  pages: {
    signIn: "/auth/signin",
    signOut: "/auth/signout",
    error: "/auth/error", // Error code passed in query string as ?error=
    verifyRequest: "/auth/verify-request", // (used for check email message)
    newUser: "/auth/register", // New users will be directed here on first sign in (leave the property out if not of interest)
  },
};

const handler = NextAuth(authOptions);

export { handler as GET, handler as POST };