Design System for Unstable Third-Party Authentication

Problem Overview

Design a reliable end-to-end request flow in which a client must first obtain an auth token from an unstable third-party authentication server, then use that token to call a main/backend server. The third-party server may return garbage/malformed responses or fail requests outright. The backend is treated as a black box…

• 4 candidate-reported follow-ups — the exact probes interviewers asked, with the trigger for each
• The rest of the problem statement — full requirements, constraints, and edge cases
• Approach and trade-offs — what passing candidates did, and the mistakes that sink people