@x402/express

Express middleware integration for the x402 Payment Protocol. This package provides a simple middleware function for adding x402 payment requirements to your Express.js applications.

Installation

``bash
pnpm install @x402/express
`

Quick Start

`typescript
import express from "express";
import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";

const app = express();

const facilitatorClient = new HTTPFacilitatorClient({ url: "https://facilitator.x402.org" });
const resourceServer = new x402ResourceServer(facilitatorClient)
.register("eip155:84532", new ExactEvmScheme());

// Apply the payment middleware with your configuration
app.use(
paymentMiddleware(
{
"GET /protected-route": {
accepts: {
scheme: "exact",
price: "$0.10",
network: "eip155:84532",
payTo: "0xYourAddress",
},
description: "Access to premium content",
},
},
resourceServer,
),
);

// Implement your protected route
app.get("/protected-route", (req, res) => {
res.json({ message: "This content is behind a paywall" });
});

app.listen(3000);
`

Configuration

The paymentMiddleware function accepts the following parameters:

`typescript
paymentMiddleware(
routes: RoutesConfig,
server: x402ResourceServer,
paywallConfig?: PaywallConfig,
paywall?: PaywallProvider,
syncFacilitatorOnStart?: boolean
)
`

$3

1. routes (required): Route configurations for protected endpoints
2. server (required): Pre-configured x402ResourceServer instance
3. paywallConfig (optional): Configuration for the built-in paywall UI
4. paywall (optional): Custom paywall provider
5. syncFacilitatorOnStart (optional): Whether to sync with facilitator on startup (defaults to true)

See the sections below for detailed configuration options.

API Reference

$3

The ExpressAdapter class implements the HTTPAdapter interface from @x402/core, providing Express-specific request handling:

`typescript
class ExpressAdapter implements HTTPAdapter {
getHeader(name: string): string | undefined;
getMethod(): string;
getPath(): string;
getUrl(): string;
getAcceptHeader(): string;
getUserAgent(): string;
}
`

$3

`typescript
function paymentMiddleware(
routes: RoutesConfig,
server: x402ResourceServer,
paywallConfig?: PaywallConfig,
paywall?: PaywallProvider,
syncFacilitatorOnStart?: boolean,
): (req: Request, res: Response, next: NextFunction) => Promise;
`

Creates Express middleware that:

1. Uses the provided x402ResourceServer for payment processing
2. Checks if the incoming request matches a protected route
3. Validates payment headers if required
4. Returns payment instructions (402 status) if payment is missing or invalid
5. Processes the request if payment is valid
6. Handles settlement after successful response

$3

Routes are passed as the first parameter to paymentMiddleware:

`typescript
const routes: RoutesConfig = {
"GET /api/protected": {
accepts: {
scheme: "exact",
price: "$0.10",
network: "eip155:84532",
payTo: "0xYourAddress",
maxTimeoutSeconds: 60,
},
description: "Premium API access",
},
};

app.use(paymentMiddleware(routes, resourceServer));
`

$3

The middleware automatically displays a paywall UI when browsers request protected endpoints.

Option 1: Full Paywall UI (Recommended)

Install the optional @x402/paywall package for a complete wallet connection and payment UI:

`bash
pnpm add @x402/paywall
`

Then configure it:

`typescript
const paywallConfig: PaywallConfig = {
appName: "Your App Name",
appLogo: "/path/to/logo.svg",
testnet: true,
};

app.use(paymentMiddleware(routes, resourceServer, paywallConfig));
`

The paywall includes:

- EVM wallet support (MetaMask, Coinbase Wallet, etc.)
- Solana wallet support (Phantom, Solflare, etc.)
- USDC balance checking
- Chain switching
- Onramp integration for mainnet

Option 2: Basic Paywall (No Installation)

Without @x402/paywall installed, the middleware returns a basic HTML page with payment instructions. This works but doesn't include wallet connections.

Option 3: Custom Paywall Provider

Provide your own paywall provider:

`typescript
app.use(paymentMiddleware(routes, resourceServer, paywallConfig, customPaywallProvider));
`

This allows full customization of the paywall UI.

For advanced configuration (builder pattern, network-specific bundles, custom handlers), see the @x402/paywall README.

Advanced Usage

$3

`typescript
app.use(
paymentMiddleware(
{
"GET /api/premium/*": {
accepts: {
scheme: "exact",
price: "$1.00",
network: "eip155:8453",
payTo: "0xYourAddress",
},
description: "Premium API access",
},
"GET /api/data": {
accepts: {
scheme: "exact",
price: "$0.50",
network: "eip155:84532",
payTo: "0xYourAddress",
maxTimeoutSeconds: 120,
},
description: "Data endpoint access",
},
},
resourceServer,
),
);
`

$3

If you need to use a custom facilitator server, configure it when creating the x402ResourceServer:

`typescript
import { HTTPFacilitatorClient } from "@x402/core/server";
import { x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";

const customFacilitator = new HTTPFacilitatorClient({
url: "https://your-facilitator.com",
createAuthHeaders: async () => ({
verify: { Authorization: "Bearer your-token" },
settle: { Authorization: "Bearer your-token" },
}),
});

const resourceServer = new x402ResourceServer(customFacilitator)
.register("eip155:84532", new ExactEvmScheme());

app.use(paymentMiddleware(routes, resourceServer, paywallConfig));
`

Migration from x402-express

If you're migrating from the legacy x402-express package:

1. Update imports: Change from x402-express to @x402/express
2. New API: Create an x402ResourceServer and register payment schemes
3. Parameter order: Routes first, then resource server, then optional paywall config

$3

`typescript
import { paymentMiddleware } from "x402-express";

app.use(
paymentMiddleware(
payTo, // First param was payTo address
routes, // Second param was routes
facilitator, // Third param was facilitator config
paywall, // Fourth param was paywall config
),
);
`

$3

`typescript
import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { HTTPFacilitatorClient } from "@x402/core/server";
import { ExactEvmScheme } from "@x402/evm/exact/server";

const facilitator = new HTTPFacilitatorClient({ url: facilitatorUrl });
const resourceServer = new x402ResourceServer(facilitator)
.register("eip155:84532", new ExactEvmScheme());

app.use(
paymentMiddleware(
routes, // First param is routes (payTo is part of route config)
resourceServer, // Second param is resource server (required)
paywallConfig, // Third param is paywall config (optional)
),
);
`

Note: The payTo` address is now specified within each route configuration rather than as a separate parameter.