Stop Losing 86% of Mobile Users: Lazy Auth with Firebase (Tutorial)

[MyrinNew]

The $300 Million Problem 💸

The famous "$300 Million Button" case study proved that forcing users to register before checkout is a revenue killer. On mobile, the stats are even worse—up to 86% of users abandon apps when hit with an immediate login wall.


The solution? Lazy Registration (or "Just-in-Time" auth).


In this quick tutorial, I’ll show you how to implement a flow where users are "logged in" anonymously first, and only asked for credentials when they want to save their work.


Step 1: Start with Anonymous Auth 👻

Firebase provides a specific method to create temporary, persisted sessions without asking the user for any data.


Docs: signInAnonymously






import { getAuth, signInAnonymously } from "firebase/auth";

const auth = getAuth();

// 1. Log them in silently
await signInAnonymously(auth);

// 2. Listen to the state (User ID persists on reload!)
auth.onAuthStateChanged((user) => {
if (user && user.isAnonymous) {
console.log("User is a Guest 👻", user.uid);
}
});








Step 2: The "Upgrade" (Account Linking) 🔗

This is the most critical part. When the user decides to sign up (e.g., to save their settings), you don't create a new account. You upgrade the existing one.


This preserves the uid and all Firestore data attached to it.


Docs: linkWithCredential






import { EmailAuthProvider, linkWithCredential } from "firebase/auth";

const upgradeAccount = async (email, password) => {
const credential = EmailAuthProvider.credential(email, password);
const user = auth.currentUser;

try {
// Merge the new credentials into the existing anonymous account
const result = await linkWithCredential(user, credential);
console.log("Guest upgraded to Permanent User! 🎉");
} catch (error) {
console.error("Error linking account:", error);
}
};








Pro Tip: Cleaning up "Ghost" Users 🧹

One downside of Anonymous Auth is that you might end up with thousands of abandoned guest accounts in your database.


You can solve this without writing a custom script by enabling Google Cloud Identity Platform. This allows you to set an automatic deletion policy (e.g., delete anonymous users inactive for 30 days).


Docs: Identity Platform Cleanup


Read the Full Guide 📘

I wrote a detailed deep dive on my personal blog that covers:

• React Hooks implementation.
• Handling credential-already-in-use errors.
• Screenshots of the Identity Platform configuration.
• A live demo using my Windows CLI learning app.

👉 Read the full article with guiding screenshots: Lazy Registrations with Firebase





Have you implemented deferred auth in your apps?




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