Canonicalizes device_id, nonce and message, computes an HMAC-SHA256 tag with caller-suppli

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0x2880EdfFF13100677Bf97A3CBdF3Bc34771C4E5E",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "2000",
    "maxTimeoutSeconds": 300
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "device_id": "sensor-berlin-17",
          "ephemeral_key": "example-ephemeral-key-2026",
          "message": "boot:4.2.1",
          "nonce": "20260831-0001"
        },
        "bodyType": "json",
        "method": "POST",
        "type": "http"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "input": {
          "additionalProperties": false,
          "properties": {
            "body": {
              "additionalProperties": false,
              "properties": {
                "claimed_tag_hex": {
                  "pattern": "^[0-9a-fA-F]{64}$",
                  "type": "string"
                },
                "device_id": {
                  "description": "Stable device identifier.",
                  "maxLength": 128,
                  "minLength": 1,
                  "type": "string"
                },
                "ephemeral_key": {
                  "description": "Ephemeral HMAC key; long-lived production keys must not be sent.",
                  "maxLength": 512,
                  "minLength": 16,
                  "type": "string"
                },
                "message": {
                  "description": "Challenge payload.",
                  "maxLength": 4096,
                  "minLength": 1,
                  "type": "string"
                },
                "nonce": {
                  "description": "Fresh caller-generated challenge nonce.",
                  "maxLength": 256,
                  "minLength": 8,
                  "type": "string"
                }
              },
              "required": [
                "device_id",
                "nonce",
                "message",
                "ephemeral_key"
              ],
              "type": "object"
            },
            "bodyType": {
              "enum": [
                "json",
                "form-data",
                "text"
              ],
              "type": "string"
            },
            "method": {
              "enum": [
                "POST",
                "PUT",
                "PATCH"
              ],
              "type": "string"
            },
            "type": {
              "const": "http",
              "type": "string"
            }
          },
          "required": [
            "type",
            "method",
            "bodyType",
            "body"
          ],
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

curl "https://iot.halowerk.com/v1/device-auth"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://iot.halowerk.com/v1/device-auth");
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://iot.halowerk.com/v1/device-auth")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header