x402 security controls for autonomous payments

What the protocol establishes

x402 turns HTTP 402 into a programmable payment flow for APIs, content and autonomous agents. Because settlement can be fast and irreversible, policy belongs before the signed payment payload is submitted.

Five checks before execution

1. Validate the payment requirements from the resource server.
2. Bind resource, network, asset, amount and payee to approved intent.
3. Apply a hard budget before creating the payment signature.
4. Use a stable payment identifier for idempotent retries.
5. Record the decision receipt before facilitator submission.

The gap MandateShield closes

An agent can correctly follow an x402 challenge that points to an unapproved payee, asset or amount. Protocol correctness alone is not user authorization.

MandateShield normalizes execution facts and returns a deterministic decision with exact findings and a tamper-evident receipt. It complements protocol-native signature verification; it does not replace it.