React Native authentication and cloud Firestore for web apps - reactjs

Question

I am new to both Firebase and React so bear with me here.
I am trying to use cloud Firestore and Authentication in my application but am a little unsure on how to set up my firebase.js file. I have scaled the internet and watched plenty of videos/tutorials but can't seem to figure out how to implement these into my app. It also seems that some tutorials that I watched from 2020 are not out of date.
Here's my code:
import { initializeApp } from "firebase/app";
import { getFirestore } from "firebase/firestore";
// import { getAuth, signInWithCustomToken } from "firebase/auth";
const firebaseConfig = {
apiKey: process.env.REACT_APP_FIREBASE_API_KEY,
authDomain: process.env.REACT_APP_FIREBASE_AUTH_DOMAIN,
projectId: process.env.REACT_APP_FIREBASE_PROJECT_ID,
storageBucket: process.env.REACT_APP_FIREBASE_STORAGE_BUCKET,
messagingSenderId: process.env.REACT_APP_FIREBASE_MESSAGING_SENDER_ID,
appId: process.env.REACT_APP_FIREBASE_APP_ID
};
// const auth = getAuth();
// signInWithCustomToken(auth, token)
// .then((userCredential) => {
// // Signed in
// const user = userCredential.user;
// // ...
// })
// .catch((error) => {
// const errorCode = error.code;
// const errorMessage = error.message;
// // ...
// });
const app = initializeApp(firebaseConfig);
const db = getFirestore(app)
// export const auth = app.auth()
export { db }

Answer 1

You can export the auth instance from firebase.js and then use it in any component you need. Assuming you have a login component:
firebase.js:
import { initializeApp } from "firebase/app";
import { getFirestore } from "firebase/firestore";
import { getAuth } from "firebase/auth"
const app = initializeApp(firebaseConfig);
const db = getFirestore(app)
const auth = getAuth(app)
export { db, auth }
login.jsx:
// login component
import { auth } from "./firebase.js"
import { signInWithEmailAndPassword } from "firebase/auth"
// run on button click or relevant events
signInWithEmailAndPassword(auth, email, password).then((user) => {
console.log(user)
})