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Welcome! In this lesson, we'll dive into managing user sessions and understanding authentication states in Firebase. These are crucial for building secure and user-friendly apps.

We'll cover how to:

• Monitor when a user logs in or out.
• Keep users logged in across app restarts.
• Update user profile information.

Firebase Authentication provides a powerful way to monitor a user's login status in real-time. This is done using an "authentication state listener."

• It tells your app if a user is currently logged in or logged out.
• It fires whenever the user's authentication state changes (e.g., login, logout, token refresh).
• This is perfect for updating UI elements or redirecting users.

Here's how you set up an authentication state listener. It's a key part of making your app react to user logins and logouts.

This example assumes Firebase is initialized and the auth service is available.

Imagine your user logs in, closes the app, and reopens it only to find they're logged out. Frustrating, right?

Firebase Auth solves this with "session persistence." It allows you to specify how long a user's login session should last, even after they close their browser or app.

• Firebase stores user credentials securely.
• It automatically re-authenticates the user when they return.

Firebase offers different levels of session persistence to suit various application needs:

• LOCAL: The user's session is persisted even if the browser window is closed. (Default for web)
• SESSION: The session is persisted only for the current browser session. It's cleared when the window is closed.
• NONE: No session persistence. The user is logged out when the page is refreshed or the app restarts.

You can set the desired persistence level before a user signs in. This tells Firebase how to handle the session for that specific login.

Here's an example of setting it to SESSION for a temporary login.

Once a user is logged in, you often need to access their information like their ID, email, or display name. Firebase makes this easy.

• The currentUser property of the auth object holds the currently logged-in user.
• It will be null if no user is logged in.
• Important: Always check currentUser inside an onAuthStateChanged listener to ensure it's up-to-date.

Firebase Auth allows users to update basic profile information directly. This includes their display name and profile photo URL.

These updates are client-side and don't require re-authentication for the user to see the changes in their own profile object.

• Use the updateProfile method on the user object.
• Common updates: displayName and photoURL.

Let's see how to update a user's display name. This is useful for personalizing their experience in your app.

This operation requires a logged-in user.

Consider a web application using Firebase Authentication. A user logs in, then closes their browser and reopens it a few minutes later. They find themselves still logged in.

Which Firebase Auth persistence setting was most likely active?

Great job! In this lesson, you learned how to effectively manage user sessions and states in your Firebase application.

• We explored onAuthStateChanged for real-time user status monitoring.
• You understood the importance of session persistence and its different levels (LOCAL, SESSION, NONE).
• Finally, you learned how to access and update a logged-in user's profile information.

These skills are fundamental for building dynamic and personalized user experiences!