Authentication Implementation
Complete guide to implementing secure authentication in AI-generated applications. Learn how to properly implement login systems, password security, session management, and token handling.
Never Build Custom Authentication
AI-generated authentication code is frequently vulnerable. Building secure authentication requires expertise in cryptography, session management, and attack vectors. Always use established authentication libraries and services like Supabase Auth, Firebase Auth, or Auth0 instead of custom implementations.
Authentication Security Checklist
Follow these 12 steps to properly implement authentication. Critical items are non-negotiable security requirements for any authentication system.
Use established authentication libraries
Never build custom authentication from scratch. Use Supabase Auth, Firebase Auth, Auth0, NextAuth.js, or Passport.js instead of rolling your own.
Hash passwords with bcrypt or argon2
Never store plaintext passwords. Use bcrypt with cost factor 12+ or argon2id for password hashing. Reject weak hash functions like MD5 or SHA1.
Implement secure session management
Use cryptographically secure session tokens, set HttpOnly and Secure flags on cookies, and implement session timeout and rotation.
Validate JWT tokens properly
Verify JWT signature, check expiration and issuer claims, and reject tokens with suspicious claims. Never trust client-provided tokens without verification.
Enforce password strength requirements
Require minimum length of 12+ characters. Check against common password lists and prevent use of leaked passwords from breaches.
Implement account lockout
Lock accounts after 5-10 failed login attempts to prevent brute force attacks. Use exponential backoff or CAPTCHA for additional protection.
Add multi-factor authentication (MFA)
Support TOTP, SMS, or email-based second factor authentication for sensitive operations and high-value accounts.
Implement secure password reset
Use time-limited, single-use tokens sent to verified email addresses. Never reset passwords via security questions or unverified channels.
Log authentication events
Record successful logins, failed attempts, password changes, and MFA enrollment for security monitoring and incident response.
Use secure random for tokens
Generate session tokens, reset tokens, and API keys using cryptographically secure random sources, not Math.random() or predictable sequences.
Implement refresh token rotation
Use short-lived access tokens with refresh tokens. Rotate refresh tokens on each use and revoke tokens on logout.
Add authentication monitoring
Alert on suspicious patterns like logins from new locations, multiple failed attempts, or unusual access times for user accounts.
Common Authentication Vulnerabilities
Weak Password Hashing
CriticalUsing MD5, SHA1, or plaintext storage instead of bcrypt or argon2, allowing attackers to easily crack stolen password databases
JWT Verification Skipped
CriticalAccepting JWT tokens without signature verification, allowing attackers to forge tokens and impersonate any user
Session Tokens in URLs
HighPassing authentication tokens in URL query parameters instead of cookies or headers, exposing them in logs and browser history
No Brute Force Protection
HighMissing rate limiting or account lockout allows unlimited login attempts, enabling credential stuffing and password guessing attacks
Related Resources
Test Your Authentication Security
VibeEval automatically tests authentication implementations for weak password hashing, JWT vulnerabilities, session hijacking, and brute force protection gaps.
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