Compute a keyed HMAC of some data with a secret key — the standard way to sign and verify

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xb3f4de103F34b99f0Da19B4F16D6B53a14C2194A",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "2000",
    "maxTimeoutSeconds": 300
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "algorithm": "sha256",
          "data": "example",
          "inputEncoding": "utf8",
          "key": "example",
          "keyEncoding": "utf8"
        },
        "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": "Digest algorithm, one of sha256, sha512, sha384, sha224, sha1, sha3-256, sha3-384, sha3-512, md5, ripemd160, blake2b512, blake2s256.",
                  "enum": [
                    "sha256",
                    "sha512",
                    "sha384",
                    "sha224",
                    "sha1",
                    "sha3-256",
                    "sha3-384",
                    "sha3-512",
                    "md5",
                    "ripemd160",
                    "blake2b512",
                    "blake2s256"
                  ],
                  "type": "string"
                },
                "data": {
                  "description": "The data to authenticate, in `inputEncoding`.",
                  "maxLength": 5000000,
                  "type": "string"
                },
                "inputEncoding": {
                  "description": "How to interpret the text as bytes (utf8, hex, base64, base64url). Default utf8.",
                  "enum": [
                    "utf8",
                    "hex",
                    "base64",
                    "base64url"
                  ],
                  "type": "string"
                },
                "key": {
                  "description": "The secret key, in `keyEncoding`.",
                  "maxLength": 16384,
                  "minLength": 1,
                  "type": "string"
                },
                "keyEncoding": {
                  "description": "How to interpret the key as bytes (utf8, hex, base64, base64url). Default utf8.",
                  "enum": [
                    "utf8",
                    "hex",
                    "base64",
                    "base64url"
                  ],
                  "type": "string"
                },
                "outputEncoding": {
                  "description": "How to render the digest (hex, base64, base64url). Default hex.",
                  "enum": [
                    "hex",
                    "base64",
                    "base64url"
                  ],
                  "type": "string"
                }
              },
              "required": [
                "data",
                "key",
                "algorithm"
              ],
              "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://hash.openverbs.com/v1/hmac"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

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