Deterministic payment-policy firewall with a signed, short-lived decision receipt

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0x7BEcA68DD9aC733D4de6b16d16B85Dc391c071e2",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "2000",
    "maxTimeoutSeconds": 60
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "intent_id": "purchase-42",
          "payment_requirement": {
            "amount": "4000",
            "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
            "maxTimeoutSeconds": 60,
            "network": "eip155:8453",
            "payTo": "0x0000000000000000000000000000000000000001"
          },
          "policy": {
            "allowed_assets": [
              "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"
            ],
            "allowed_networks": [
              "eip155:8453"
            ],
            "allowed_recipients": [
              "0x0000000000000000000000000000000000000001"
            ],
            "max_amount": "5000",
            "max_timeout_seconds": 90
          }
        },
        "bodyType": "json",
        "discoverable": true,
        "method": "POST",
        "type": "http"
      },
      "inputSchema": {
        "required": [
          "payment_requirement",
          "policy"
        ],
        "type": "object"
      },
      "output": {
        "example": {
          "decision": {
            "decision": "allow",
            "reasons": [],
            "valid_until": 0
          },
          "receipt": {
            "signature": "base64url"
          }
        },
        "type": "json"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "type": "object"
    }
  }
}

curl "https://phion.systems/v1/paid/preflight-payment"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://phion.systems/v1/paid/preflight-payment");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

import httpx
res = httpx.get("https://phion.systems/v1/paid/preflight-payment")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header