How to store user info on firestore using adapter with next-auth v4+?

How can we store user info on firestore automatically when user sign up. Looking for built in method like adapters in next-auth to avoid mistakes in storing info efficiently. Doc tutorials uses prisma and mongo as example but I am looking for storing it on firestore.

There is canary version of firebase adapter with next-auth v5 beta. But it throws error as I'm using latest firebase in my project already. Apart from version issue there is error like r is not function... when i use v5 beta (5.0.0-beta.25) similar question for this error

doc ref https://authjs.dev/getting-started/adapters/firebase

By the way the firebase adapter uses firebase sdk which is client sdk. So this way we are using client sdk on server side in nextjs. I wonder how they are using firebase client sdk on server side of nextjs.

Here is simple way to do so.

Step 1 : create config file and initialize firebase admin app to use firestore instance
Step 2 : create route js and pass firestore instance to firestore adapter in auth options. that's it!

Initialize NextAuth.js with a Route Handler. Here I am taking two providers Google and Github with firestore adapter to store user info.

Step 1 (You can ignore and use your own existing config to get firestore instance )
Initialize firebase-admin app and export the instance of firestore (or follow your own way to initialize and use firestore instance directly in route.js).

import { PROJECT_ID } from '../firebase/constants/project';
import serviceAccount from './secrets/ServiceAccount77.json';

import admin from 'firebase-admin';
import { getApps } from 'firebase-admin/app';
import { getFirestore } from 'firebase-admin/firestore';


if (!getApps().length) {

  admin.initializeApp({
    credential: admin.credential.cert(serviceAccount),
    projectId: PROJECT_ID,
    storageBucket: `${PROJECT_ID}.appspot.com`,
  });

}

const db = getFirestore();

export { admin, db };

Step 2 :
api/auth/[...nextauth]/route.js

import NextAuth from "next-auth"
import GithubProvider from "next-auth/providers/github"
import GoogleProvider from "next-auth/providers/google"
import { FirestoreAdapter } from "@auth/firebase-adapter"
import { db } from '@/lib/firebase/config';

export const authOptions = {
  adapter: FirestoreAdapter(db),
  providers: [
    GoogleProvider({
      clientId: process.env.GOOGLE_ID,
      clientSecret: process.env.GOOGLE_SECRET,
    }),
    GithubProvider({
      clientId: process.env.GITHUB_ID,
      clientSecret: process.env.GITHUB_SECRET,
    }),
    // ...add more providers here
  ],
}

const handler = NextAuth(authOptions)
export { handler as GET, handler as POST }

This is basic setup creates user related info on firestore. Current version and configs creates collections as sessions, accounts and users. See screenshots

Result

collection - account

collection - sessions

collection - user

Version i used while trying it

"firebase-admin": "^12.7.0",
"next": "^14.2.5",
"next-auth": "^4.24.10",
"react": "^18.3.1",
"@auth/firebase-adapter": "^2.7.3",