How to Implement an Authentication System
Build a complete authentication system with email, social login, MFA, and session management from scratch.
What You'll Learn
This intermediate-level guide walks you through how to implement an authentication system step by step. Estimated time: 16 min.
Step 1: Design the auth architecture
Plan your authentication flow including registration, login, password reset, email verification, and session management.
Step 2: Implement secure password handling
Use bcrypt or Argon2 for password hashing, enforce complexity requirements, and implement breach detection with HaveIBeenPwned.
Step 3: Add social OAuth providers
Integrate Google, GitHub, and Apple sign-in using the Authorization Code flow with PKCE for secure token exchange.
Step 4: Implement multi-factor authentication
Add TOTP-based MFA with authenticator apps, SMS fallback, and recovery codes for account recovery.
Step 5: Build session management
Create secure session handling with HTTP-only cookies, refresh token rotation, device tracking, and remote session revocation.
Frequently Asked Questions
Should I build auth myself or use a service?▾
Use a managed service like Clerk, Auth0, or Supabase Auth for most projects. Build custom only when you need unusual flows or want to avoid vendor lock-in.
How do I store sessions securely?▾
Use HTTP-only, Secure, SameSite cookies for web sessions. Store refresh tokens server-side. Implement token rotation and short access token lifetimes.
What is the most important security measure?▾
Rate limiting on login endpoints prevents brute force attacks and is the single most impactful security measure. Combine with account lockout after failed attempts.