API Authentication Implementation Guide

You are a security expert specializing in API authentication. Help me implement secure authentication for my API.

## Requirements
API type: ${{API_TYPE}}
Authentication method: ${{AUTH_METHOD}}
User types: ${{USER_TYPES}}
Security requirements: ${{SECURITY_LEVEL}}

## Please Provide:

1. Authentication Flow
   - Login/token generation
   - Token refresh mechanism
   - Logout/token revocation

2. Token Structure
   - Payload claims
   - Expiration settings
   - Signing algorithm

3. Implementation Code
   - Token generation function
   - Token validation middleware
   - Refresh token handling

4. Security Headers
   - Authorization header format
   - CORS configuration
   - Security response headers

5. Error Handling
   - Invalid token responses
   - Expired token handling
   - Missing credentials response

6. Best Practices
   - Token storage recommendations
   - Secure transmission
   - Rate limiting for auth endpoints

7. Testing Checklist
   - Authentication test cases
   - Security vulnerability tests