OAuth 2.0 enables secure delegated authorization. Implementing it correctly is crucial for security. Here's how to do it right.
OAuth Flows
Authorization Code (with PKCE):
- Best for web and mobile apps
- Most secure
- Server exchanges code for tokens
Client Credentials:
- Machine-to-machine
- No user involvement
- Service accounts
Implicit (Deprecated):
- Don't use for new apps
- Tokens exposed in URL
- Replaced by Auth Code + PKCE
Resource Owner Password:
- Legacy systems only
- User credentials sent to client
- Avoid if possible
Authorization Code Flow with PKCE
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OAuth Server Implementation
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Token Validation
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Refresh Token Rotation
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Best Practices
Security:
✓ Always use PKCE
✓ Validate redirect URIs exactly
✓ Use short-lived access tokens
✓ Rotate refresh tokens
✓ Store tokens securely
Implementation:
✓ Use state parameter against CSRF
✓ Validate all inputs
✓ Log security events
✓ Rate limit token endpoints
Token Handling:
✓ Never expose tokens in URLs
✓ Use HttpOnly cookies when possible
✓ Clear tokens on logout
✓ Implement token revocation
Conclusion
OAuth 2.0 requires careful implementation. Use Authorization Code with PKCE, validate everything, rotate refresh tokens, and follow security best practices. When possible, use proven libraries rather than implementing from scratch.