Phase 6: Building With Real Data · 30 min · Supabase · Cursor · Claude Code
Authentication Patterns
Auth is the gate between 'my data' and 'your data.' Get it right.
Hiring signal: What changes when you use this: you can add login/signup to your app — which means users get their own private data.
What you will learn
- Understand the auth flow: signup, login, session, logout
- Set up Supabase Auth in your app
- Implement protected routes that redirect unauthenticated users
- Store and check the session
- Recognize common auth mistakes in AI-generated code
Your Mission
Implement signup, login, session check, auth state listener, logout, and a protected route — then audit for common auth mistakes. Output: auth_setup.md.
You need: A Supabase-connected app (from Lesson 02).
Time: 35 minutes.
Step 1: Learn the Auth Flow (5 min)
The complete auth flow has 4 parts:
- Signup: User creates account → Supabase creates user + returns session
- Login: User enters credentials → Supabase verifies + returns session
- Session: Token persists across refreshes → app checks session to know if logged in
- Logout: User signs out → session destroyed → redirect to login
Client-side vs. server-side protection
Auth has two layers: (1) Client-side — frontend checks if user is logged in, redirects to login if not. This is UX. (2) Server-side — RLS policies on the database restrict data access. This is security. You need BOTH. Client-side only: a user can bypass the frontend and query the database directly. Server-side only: users see pages they shouldn't before being redirected.
Unlock the full lesson
You've read the first 2 sections. The rest of this lesson covers Step 2: Implement Signup and Login (10 min), Auth Forms, Step 3: Add Session Check and Auth State Listener (5 min), Session Management, Step 4: Create a Protected Route (5 min), Protected Route, Step 5: Test the Full Flow (5 min), Flow Test, Step 6: Audit for 5 Common Auth Mistakes (5 min), Auth Mistake Audit, You're Done — plus a hands-on lab, quiz, and project artifact.
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