Design a Global Authentication Token Service

To design a global authentication token service for a platform like Airbnb, I would prioritize low latency and strict security. First, we generate JSON Web Tokens signed asymmetrically. The private signing key resides in a highly secure, centralized KMS, while public verification keys are cached at the edge in every region to avoid cross-region round trips. This ensures validation happens locally within milliseconds. For expiration, we issue short-lived access tokens, say 15 minutes, paired with longer refresh tokens. If a user needs to revoke access immediately, such as when a device is lost, we cannot rely solely on token expiration. Instead, we implement a lightweight revocation list stored in a globally distributed cache like DynamoDB Global Tables or Redis Cluster. When a token is presented, the edge node checks this cache first. To handle key rotation without downtime, we support multiple active versions of the public key, allowing seamless transition. Finally, we monitor for anomalies; if a single IP generates thousands of valid tokens, our system triggers an automatic lockout. This approach balances the need for speed in a travel app with the rigorous security required for financial transactions.