Generate an RFC 4226 counter-based HMAC one-time password from a base32 secret and counter

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xb3f4de103F34b99f0Da19B4F16D6B53a14C2194A",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "4000",
    "maxTimeoutSeconds": 300
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "algorithm": "SHA1",
          "counter": 1,
          "digits": 6,
          "secret": "example"
        },
        "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": {
                "algorithm": {
                  "description": "HMAC algorithm. Default SHA1.",
                  "enum": [
                    "SHA1",
                    "SHA256",
                    "SHA512"
                  ],
                  "type": "string"
                },
                "counter": {
                  "description": "The HOTP counter value.",
                  "minimum": 0,
                  "type": "integer"
                },
                "digits": {
                  "description": "Number of code digits. Default 6.",
                  "maximum": 10,
                  "minimum": 6,
                  "type": "integer"
                },
                "secret": {
                  "description": "Base32-encoded shared secret.",
                  "maxLength": 1024,
                  "minLength": 1,
                  "type": "string"
                }
              },
              "required": [
                "secret",
                "counter"
              ],
              "type": "object"
            },
            "bodyType": {
              "enum": [
                "json",
                "form-data",
                "text"
              ],
              "type": "string"
            },
            "method": {
              "enum": [
                "POST"
              ],
              "type": "string"
            },
            "type": {
              "const": "http",
              "type": "string"
            }
          },
          "required": [
            "type",
            "method",
            "bodyType",
            "body"
          ],
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

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

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