Refresh Tokens
Refresh Token Flow
1. Access token expires (15 min)
2. Client sends refresh token to /auth/refresh
3. Server validates refresh token
4. Server issues new access token (+ new refresh token)
5. Old refresh token is invalidated
Refresh Token Storage
- Store in HttpOnly cookie (most secure)
- Or store in secure storage on client
- Never in localStorage (XSS vulnerable)
Token Rotation
Each refresh issues new tokens and invalidates old ones. Prevents token reuse attacks.
Key Points
- Understanding Refresh Tokens is essential for production systems
- Always consider scalability and maintainability
- Test thoroughly before deploying to production
- Monitor performance and set up alerting
Common Patterns
- Validation: Always validate input at the boundary
- Error Handling: Use structured error responses
- Logging: Log key events for debugging
- Testing: Unit, integration, and load tests
- Documentation: Keep docs updated with code changes
Token Management
Token Lifecycle
- Generation: Create with short expiry
- Validation: Verify signature and claims
- Refresh: Exchange refresh token for new access token
- Revocation: Invalidate on logout/security events
Storage
- Access tokens: Memory or short-lived storage
- Refresh tokens: Secure HTTP-only cookies
- Revoked tokens: Redis blacklist with TTL
Best Practices
- Rotate signing keys regularly
- Implement token binding
- Monitor token usage patterns
Key Points
- Understanding Refresh Tokens is essential for production systems
- Always consider scalability and maintainability
- Test thoroughly before deploying to production
- Monitor performance and set up alerting
Common Patterns
- Validation: Always validate input at the boundary
- Error Handling: Use structured error responses
- Logging: Log key events for debugging
- Testing: Unit, integration, and load tests
- Documentation: Keep docs updated with code changes
Practice Problems
Design and implement a solution for Refresh Tokens in a backend system. Consider scalability, error handling, and production readiness.
Solution
// Refresh Tokens implementation
// Key aspects: validation, error handling, logging, testing
public class RefreshTokens {
// Production-ready implementation
}Identify and handle edge cases for Refresh Tokens. What happens under high load, with invalid input, or during failures?
Solution
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotencyWrite a testing strategy for Refresh Tokens. Include unit tests, integration tests, and performance tests.
Solution
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injectionQuiz
1. Refresh token should be stored in?
2. Token rotation means?
3. What is the primary purpose of Refresh Tokens?
4. What is a common mistake when implementing Refresh Tokens?
Flashcards
Question
Where to store refresh token?
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Answer
HttpOnly cookie (most secure)
Question
Token rotation?
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Answer
New tokens each refresh, old invalidated
Question
What is Refresh Tokens?
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Answer
Refresh Tokens is a key concept in backend development.
Question
When to use Refresh Tokens?
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Answer
Use Refresh Tokens when building production systems that require reliability, scalability, and maintainability.
Question
Refresh Tokens best practices
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Answer
Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.
Revision Notes
Key Takeaways
- 1.Refresh tokens enable long-lived sessions
- 2.Store in HttpOnly cookie
- 3.Token rotation prevents reuse attacks
- 4.Longer lifetime than access tokens
Interview Tips
- •Implement refresh token flow
- •Know storage best practices
Cheat Sheet
Refresh Tokens
- Enable long-lived sessions
- Store: HttpOnly cookie
- Rotation: new tokens each refresh
- Longer lifetime than access tokens