Auth System
Reported by candidates from TikTok's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
You've got a TikTok design problem on your hands. March 2024 reports show they're asking about Auth System design, and that's a live-coding systems interview, not an algorithm grind. You need to think like an architect, not a coder. The OA will test how you break down a real-world problem, handle edge cases, and defend your choices under pressure. StealthCoder is your safety net if you freeze on the technical details.
Pattern and pitfall
Auth System design is about trade-offs. You'll likely need to sketch out registration, login, token management, and session handling. The trick is knowing what to include and what to skip. Candidates often overthink security (salting, hashing algorithms) or underthink scalability (token refresh logic, logout consistency). The pattern is design, which means the interviewer cares more about your reasoning than your perfect code. Walk through the data model, explain your token strategy (JWT vs. sessions), handle concurrent requests, and address potential attacks. StealthCoder can help you nail the concrete implementation details if you blank on syntax or library calls during the live OA.
If this hits your live OA and you blank, StealthCoder solves it in seconds, invisible to the proctor.
You can drill Auth System cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it.
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TikTok reuses patterns across OAs. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Auth System FAQ
Should I use JWT or session-based auth?+
JWT is stateless and scales well for distributed systems. Sessions need a shared store but are simpler to revoke. For a design problem, pick one, explain the trade-off, and stick with it. The interviewer wants to see your thinking, not religious commitment to either approach.
How deep should I go into password hashing?+
Name bcrypt or Argon2, explain why (salted, iterated, slow by design). Don't spend 10 minutes on SHA variants. Your interviewer cares that you know hashing exists and why it matters, not the exact algorithm constants.
What about token expiration and refresh?+
Short-lived access tokens (15 min) and longer-lived refresh tokens (days/weeks) is the standard. Explain how a client uses the refresh token to get a new access token without re-entering credentials. This is a real edge case TikTok cares about.
Do I need to code the entire system?+
No. Sketch the architecture, write pseudo-code or a single critical function, then describe the rest. The OA is testing design thinking. A clean DB schema and clear API contracts matter more than a complete, runnable system.
How should I handle concurrent logins on the same account?+
Decide upfront: allow one session per user or many. If one, track active session ID and invalidate old ones on new login. If many, track a list of sessions. State this assumption early so you're not caught off-guard mid-interview.