3.4 – Add User Authentication (Sign In) Lesson

Lesson Overview

Authenticating users is a foundational step in building modern web and mobile apps, especially those that handle personal data. In this lesson, you’ll learn how to set up user authentication using Supabase, a backend service that manages users, passwords, and sign-in flows out of the box. By implementing sign-in and sign-up with Supabase auth, you can make sure each user's workouts are private and tied to their account—vital for any product where users expect to “see their own stuff.”

This lesson solves the challenge of associating data with specific users and protecting it from unauthorized access. If your users can’t sign in, your app can’t deliver tailored experiences or keep data secure. Here you’ll see how Supabase handles email/password sign-ins and learn about other built-in options like Google or other providers, with pointers to explore further.

Entrepreneurs, solo founders, and small product teams will find this lesson especially useful when building SaaS tools, fitness trackers, or any product involving personal user data. Real-world examples include mobile fitness apps, project management tools, and personalized dashboards—anywhere user authentication is essential.

Who This Is For

Setting up authentication applies to anyone preparing an app for real users. You’ll benefit from this lesson if you are:

• Entrepreneurs launching user-focused web or mobile products
• Developers new to authentication systems
• Product managers prototyping applications requiring secure access
• Fitness tech creators building personalized workout trackers
• Makers interested in learning how to protect users’ data within their apps
• Teams aiming to move beyond basic local-app prototypes to real deployments

Where This Fits in a Workflow

Adding user authentication typically follows creating your data models (like the workouts table) and comes before advanced personalization or AI features. You’ll use these skills anytime you want to store or display user-specific data, such as:

• Letting a user see, save, or update their own workout history
• Restricting access so only logged-in users can view certain pages or data
• Preparing your app for scalable growth with multiple users and secure data boundaries

For example, once authentication is in place, you can easily add features like user profiles, data sharing, or AI-powered recommendations that act on each individual’s activity—all anchored to a secure identity system.

Technical & Workflow Benefits

Before adding authentication, any data stored in your workouts table would be visible or modifiable by anyone using the app—a non-starter for privacy or scaling to many users. By using Supabase auth, you remove the manual work of building an authentication system from scratch (which typically involves custom password handling, session storage, and security risks).

With authentication, every workout entry is linked to a unique user ID, ensuring that users see only their data. Switching from manual checks or shared access to automated Supabase-powered login saves setup time, reduces security risks, and helps prevent common bugs. For projects where protecting user data matters, this approach keeps your app ready for public launch much faster and with greater confidence in the integrity of each user’s experience.

Practice Exercise

Try implementing authentication using Supabase in your own development project:

1. Set up a simple web or mobile app where users can log in or register with an email and password.
2. Connect this authentication flow to a database table (like a “workouts” table) and make sure that a user can only see or add their own records.
3. Test signing up, confirming your email, logging in, saving data, and then logging out to verify that the data access works as expected.

Reflect: After logging out, can you still access any workouts? What happens if you try to save or display data while signed out?

Course Context Recap

This lesson moves you from anonymous interaction to secure, personalized experiences—right after you set up your first data structures. You’ve now linked users and their data, and are ready to expand your application’s capabilities. Up next, look for lessons on expanding database interactions and introducing AI features. Keep progressing through the course to unlock more advanced app development skills and see how authentication unlocks richer, user-focused experiences throughout your project.