In this lesson, you will learn how to provide persistent, personalized experiences to unauthenticated users by utilizing ephemeral identifiers.
Understanding Anonymous Sessions
Often, you want to allow users to interact with your application—such as building a shopping cart or saving preferences—without forcing them to create an account immediately. If we simply rely on the browser's volatile state, the user loses their data the moment they refresh or close their tab.
To solve this, we use ephemeral identifiers. Instead of requiring a formal identity, the server issues a cryptographically secure, random string (like a UUID) to the user’s browser. This identifier is stored in a secure cookie, acting as a "temporary passport."
Implementing the Identifier
When a user lands on your site, you check for this identifier. If it doesn't exist, you generate one and attach it to the response header:
const { v4: uuidv4 } = require('uuid');
app.use((req, res, next) => {
if (!req.cookies.guest_id) {
const guestId = uuidv4();
res.cookie('guest_id', guestId, {
httpOnly: true,
secure: true,
sameSite: 'Strict',
maxAge: 24 * 60 * 60 * 1000 // 24-hour lifespan
});
req.guestId = guestId;
} else {
req.guestId = req.cookies.guest_id;
}
next();
});
By associating this guest_id with records in your database (e.g., carts or drafts), you allow the user to return later and find their work waiting for them.
Bridging to Authentication
The power of this pattern shines during conversion. When an anonymous guest eventually decides to sign up or log in, you simply link the data associated with their guest_id to their new, permanent user_id. You might update the database records: db.carts.update({ guestId: req.guestId }, { userId: newUser.id }).
Crucially, treat these sessions as ephemeral. Set short expiration times and ensure they can be easily cleared or rotated. Since these are not tied to PII, you minimize the risks associated with long-lived, unauthenticated tracking, while still delivering a frictionless user experience.
Key Takeaway: Ephemeral identifiers allow you to bridge the gap between anonymous browsing and registered identity by using secure, temporary cookies to persist data without requiring immediate authentication.