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Interview question · Application & API Security

Practical coding: build a web crawler, start simple, then make it concurrent and safe.

A classic coding round with a security twist: the crawler fetches URLs that strangers wrote. The scored answer gets concurrency right, then adds scope, limits and SSRF protection.

mediumNewPreparation tags: Google, Microsoft, AmazonUpdated Nov 2026

A classic coding round with a security twist: the crawler fetches URLs that strangers wrote. The scored answer gets concurrency right, then adds scope, limits and SSRF protection.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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Every worked answer in all 17 topics, every lesson in every course, the full concept curriculum, the complete practice-test bank, and the downloadable security field guides.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

A team builds a crawler that fetches URLs supplied by users, to collect pages for an AI feature's retrieval index.

  1. What is the basic design?
  2. Why is every URL attacker input?
  3. How do you block internal destinations?
  4. What limits keep it safe and polite?
  5. What about the content collected?
  6. How would you build the crawler safely?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
Next in this trackWalk through the security attributes of a session cookie: Secure, HttpOnly, SameSite, Domain, Path and the __Host- prefix.Next in this trackDesign the session lifecycle for a web app: creation, rotation, timeouts, logout and revocation after a password change.Next in this trackWhat is clickjacking, why don't JavaScript frame-busters fix it, and what does?
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