Hono Seller

A lightweight seller agent built with Hono that monetizes a photo gallery API. AI agents discover the seller via its A2A agent card, pay USDC on Base, and receive a JWT to access protected photo endpoints.

What It Demonstrates

Mounting the Key0 payment gateway on a Hono app with key0App
Defining multiple pricing plans with different prices and access durations
Issuing JWTs with plan-specific TTLs via AccessTokenIssuer
Protecting downstream routes with honoValidateAccessToken middleware

Architecture

Agent                          Hono Seller
  |                                |
  |-- GET /.well-known/agent.json -|  (discover capabilities)
  |-- GET /discover ------------->|  (browse plans and pricing)
  |<-------- plan catalog ---------|  (planIds, amounts, wallet)
  |-- POST /x402/access ---------->|  (request access, planId)
  |<-------- X402Challenge --------|  (amount, destination, chainId)
  |                                |
  |  ... pays USDC on-chain ...    |
  |                                |
  |-- POST /x402/access ---------->|  (submit payment proof)
  |<-------- AccessGrant ----------|  (JWT + resource endpoint)
  |                                |
  |-- GET /api/photos/:id -------->|  (Bearer token)
  |<-------- photo data -----------|

Prerequisites

Bun v1.0+
A wallet address to receive USDC payments

This example omits store and seenTxStore from the key0App options for brevity. In practice, createKey0() (used internally) throws if these are missing — RedisChallengeStore and RedisSeenTxStore (or their Postgres equivalents) are required for the server to start. See the Storage guide for setup instructions.

Key Files

The entire example is a single file:

examples/hono-seller/
├── server.ts          # Hono app with Key0 payment gateway
├── package.json
└── .env.example

Code Walkthrough

1. Imports and configuration

import type { NetworkName } from "@key0ai/key0";
import { AccessTokenIssuer, X402Adapter } from "@key0ai/key0";
import { honoValidateAccessToken, key0App } from "@key0ai/key0/hono";
import { Hono } from "hono";

const PORT = Number(process.env["PORT"] ?? 3001);
const NETWORK = (process.env["KEY0_NETWORK"] ?? "testnet") as NetworkName;
const WALLET = (process.env["KEY0_WALLET_ADDRESS"] ??
  "0x0000000000000000000000000000000000000000") as `0x${string}`;
const SECRET =
  process.env["KEY0_ACCESS_TOKEN_SECRET"] ?? "dev-secret-change-me-in-production-32chars!";

All configuration comes from environment variables with safe defaults for local development. The @key0ai/key0/hono subpath export provides Hono-specific helpers.

2. Payment adapter and token issuer

const adapter = new X402Adapter({
  network: NETWORK,
  rpcUrl: process.env["KEY0_RPC_URL"],
});

const tokenIssuer = new AccessTokenIssuer(SECRET);

X402Adapter handles on-chain verification of USDC transfers on Base. AccessTokenIssuer signs and verifies JWTs using the shared secret.

3. Payment gateway

const gate = key0App({
  config: {
    agentName: "Photo Gallery Agent",
    agentDescription: "Purchase access to premium photos via USDC payments on Base",
    agentUrl: `http://localhost:${PORT}`,
    providerName: "Example Corp",
    providerUrl: "https://example.com",
    walletAddress: WALLET,
    network: NETWORK,
    challengeTTLSeconds: 900,
    plans: [
      {
        planId: "single-photo",
        unitAmount: "$0.10",
        description: "Single photo — 1 hour access",
      },
      {
        planId: "full-album",
        unitAmount: "$1.00",
        description: "Full album — 24 hour access",
      },
    ],
    // ...fetchResourceCredentials shown below
  },
  adapter,
});

key0App returns a Hono sub-app that mounts the A2A agent card at /.well-known/agent.json and the x402 payment endpoint at POST /x402/access. The plans array defines two tiers — a single photo for $0.10 and a full album for $1.00.

4. Token issuance

fetchResourceCredentials: async (params) => {
  const ttl = params.planId === "single-photo" ? 3600 : 86400;
  return tokenIssuer.sign(
    {
      sub: params.requestId,
      jti: params.challengeId,
      resourceId: params.resourceId,
      planId: params.planId,
      txHash: params.txHash,
    },
    ttl,
  );
},

fetchResourceCredentials runs after payment verification succeeds, minting a JWT with a plan-appropriate lifetime — 1 hour for single photos, 24 hours for full albums.

5. Payment lifecycle hook

The optional onPaymentReceived callback fires after a payment is verified and a credential is issued. Use it for logging, analytics, or notifying downstream systems:

onPaymentReceived: async (grant) => {
  console.log(`[Payment] Received payment for ${grant.resourceId} (${grant.planId})`);
  console.log(`  TX: ${grant.explorerUrl}`);
},

6. Protecting routes with JWT middleware

const app = new Hono();
app.route("/", gate);

const api = new Hono();
api.use("/*", honoValidateAccessToken({ secret: SECRET }));

api.get("/photos/:id", (c) => {
  const photoId = c.req.param("id");
  return c.json({
    id: photoId,
    url: `https://cdn.example.com/photos/${photoId}.jpg`,
    title: `Premium Photo ${photoId}`,
    resolution: "4K",
  });
});

app.route("/api", api);

The /api sub-router is gated by honoValidateAccessToken. Any request without a valid Bearer token receives a 401. The middleware is independent of the payment flow — it only verifies JWTs signed by the same secret.

7. Server export

export default {
  port: PORT,
  fetch: app.fetch,
};

Bun picks up the default export automatically. No explicit serve() call needed.

Running the Example

Install dependencies

cd examples/hono-seller
bun install

Configure environment

cp .env.example .env

Edit .env and set your wallet address:

.env

KEY0_WALLET_ADDRESS=0xYourWalletAddress
KEY0_ACCESS_TOKEN_SECRET=your-secret-at-least-32-characters-long
KEY0_NETWORK=testnet

Start the server

bun run start

Expected Output

Photo Gallery Agent (Hono) running on http://localhost:3001
  Agent card: http://localhost:3001/.well-known/agent.json
  x402 endpoint: http://localhost:3001/x402/access
  Network: testnet
  Wallet: 0xYour...Address

Verify the agent card

curl http://localhost:3001/.well-known/agent.json | jq .

This returns the auto-generated A2A agent card describing the seller’s capabilities, pricing plans, and payment endpoint URL.

Complete a payment flow

Run an agent against this seller to execute a full discovery, payment, and resource access cycle. When a payment completes, you will see:

[Payment] Received payment for photo-1 (single-photo)
  TX: https://sepolia.basescan.org/tx/0x...

Hono vs Express

The Key0 integration surface is nearly identical across frameworks. The main differences:

	Hono	Express
Gateway mount	`key0App()` returns a Hono sub-app	`key0Router()` returns an Express router
Token middleware	`honoValidateAccessToken()`	`validateAccessToken()`
Import path	`@key0ai/key0/hono`	`@key0ai/key0/express`
Server	`export default { fetch }`	`app.listen(port)`

For full integration documentation, see the Hono integration guide.

Source code

examples/hono-seller/server.ts

​What It Demonstrates

​Architecture

​Prerequisites

​Key Files

​Code Walkthrough

​1. Imports and configuration

​2. Payment adapter and token issuer

​3. Payment gateway

​4. Token issuance

​5. Payment lifecycle hook

​6. Protecting routes with JWT middleware

​7. Server export

​Running the Example

​Expected Output

​Verify the agent card

​Complete a payment flow

​Hono vs Express

Source code

What It Demonstrates

Architecture

Prerequisites

Key Files

Code Walkthrough

1. Imports and configuration

2. Payment adapter and token issuer

3. Payment gateway

4. Token issuance

5. Payment lifecycle hook

6. Protecting routes with JWT middleware

7. Server export

Running the Example

Expected Output

Verify the agent card

Complete a payment flow

Hono vs Express