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Interview question · Agent, Tool & MCP Security

When an AI agent buys things for users, how do payment protocols prove consent, cap spending and let merchants trust the agent?

Giving an agent a card number is the wrong design. The scored answer separates consent, spending limits and agent identity, and shows how 2025-26 protocols handle each.

hardNewPreparation tags: Google, OpenAI, StripeUpdated Nov 2026

Giving an agent a card number is the wrong design. The scored answer separates consent, spending limits and agent identity, and shows how 2025-26 protocols handle each.

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  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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What if · the follow-ups in this answer

The answer works through 4 follow-ups like an interviewer would

A travel assistant can book hotels for users while they are away, using a stored card. After a user asks for 'a cheap hotel near the conference', the agent books a non-refundable suite at four times the usual price on a site the user has never used.

  1. What was missing from this design?
  2. How would you redesign the delegation?
  3. What does the payment credential look like now?
  4. How do you summarise agent payment security?

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.

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