Henry Labs – Interview: Payment Processor

A lightweight payments SDK for creating and confirming checkouts, with built-in webhook support and an embeddable checkout UI.

This SDK simulates a real-world payment processing system, including:

• Fraud detection
• Transient system errors
• Retry scenarios
• Asynchronous authorization flows

It is designed to test robustness, error handling, and webhook integration.

Installation

bun install

Build:

bun run build

Overview

The SDK provides:

• Checkout creation
• Checkout confirmation
• Webhook endpoint registration
• Embeddable checkout UI (frontend)
• API key validation

The system performs internal validation, fraud screening, and simulated load conditions.

Operations may:

• Succeed immediately
• Resolve asynchronously
• Require retries
• Fail due to fraud controls
• Fail due to temporary system overload

Usage

Initialize (Backend)

import { PaymentProcessor } from '@henrylabs-interview/payments';

const processor = new PaymentProcessor({
	apiKey: ...,
});

Checkout API

Available under:

processor.checkout;

Create a Checkout

const response = await processor.checkout.create({
	amount: 1000,
	currency: 'USD',
	customerId: 'cust_123',
});

Confirm a Checkout (Backend)

const response = await processor.checkout.confirm({
	checkoutId: ...,
	type: 'raw-card',
	data: {
		number: ...,
		expMonth: XX,
		expYear: XXXX,
		cvc: XXX,
	},
});

Embedded Checkout (Frontend)

The SDK provides an optional embeddable checkout UI for collecting card details in the browser.

Initialize Embedded Checkout

import { EmbeddedCheckout } from '@henrylabs-interview/payments';

const embedded = new EmbeddedCheckout({
	checkoutId: 'chk_123',
});

Render Embedded Checkout

embedded.render('#checkout-container', (paymentToken) => {
	console.log('Received payment token:', paymentToken);

	// Send token to backend for confirmation
});

Parameters

| Parameter | Description | | -------------------- | ------------------------------------- | | containerElementId | ID of DOM element to render into | | callbackFn | Called with a generated payment token |

Behavior

• Renders a secure card collection UI
• Collects card number, expiry, and CVC
• Generates a payment token
• Returns the token via callback
• Token should be sent to your backend for confirmation

The embedded checkout is intended for browser environments only.

Webhooks

Available under:

processor.webhooks;

Register Webhook Endpoint

processor.webhooks.createEndpoint({
	url: 'https://example.com/webhooks',
	event: 'checkout.confirm',
	secret: 'whsec_...',
});

Webhook Events

Events may be emitted for:

• checkout.create
• checkout.confirm
• checkout.success
• checkout.failure

Events are triggered for:

• Immediate outcomes
• Asynchronous resolutions
• Retry scenarios

Webhook Security

If a secret is provided:

• Deliveries are signed
• Consumers must verify signatures
• Handlers must be idempotent

Retries may occur if delivery fails.

Disclaimer

This SDK is intended for evaluation and sandbox purposes only.

It does not process real payments and should not be used in production.