AP2 with A2A Protocol - Complete Implementation

Full demonstration of Agent Payments Protocol (AP2) with full Agent-to-Agent (A2A) communication

This project showcases a complete, working implementation of Google's Agent Payments Protocol (AP2) with real A2A message exchange, cryptographic JWT signatures, AI agents, and actual payment processing. Experience the future of agentic commerce!

What is AP2?

Agent Payments Protocol (AP2) is an open protocol for the emerging Agent Economy, designed to enable secure, reliable, and interoperable agent commerce. It uses Verifiable Digital Credentials (VDCs) to engineer trust in AI-driven transactions.

Key Concepts Demonstrated:

• Intent Mandate: Captures user's purchase intent with explicit consent
• Cart Mandate: Merchant-signed guarantee of items and pricing
• Payment Mandate: Cryptographically signed payment authorization
• Agent-to-Agent Communication: Shopping Agent, Merchant Agent, and Credentials Provider collaboration

What Makes This Special

This is a implementation features:

Real A2A Protocol

• Actual agent-to-agent message exchange between Shopping Agent, Merchant Agent, and Credentials Provider
• Visual A2A message log showing all inter-agent communication
• Proper A2A message structure with TextPart and DataPart

Real Cryptographic Security

• JWT signatures on Cart Mandates (merchant authorization)
• JWT signatures on Payment Mandates (user authorization)
• SHA-256 hashing for mandate integrity
• Complete audit trail with non-repudiable proof

Real AI Agent

• LangChain-powered Shopping Agent using Moonshot AI Kimi K2 (via OpenRouter)
• Natural language understanding of vacation preferences
• Intelligent package matching and recommendations

Real Payment Processing

• Stripe integration in test mode
• W3C Payment Request API compliance
• Full payment flow from intent to confirmation

Beautiful, Transparent UI

• Watch agents communicate in real-time
• See the exact data structures (mandates) being exchanged
• Visual step-by-step transaction flow
• Modern, responsive design with Chakra UI v3

Quick Start

Prerequisites

• Node.js 20 or later
• npm or yarn
• OpenRouter API key (get free at openrouter.ai/keys)
• Stripe test account (sign up at stripe.com)

Installation

1. Install dependencies:

npm install
# or
yarn install

1. Set up environment variables:

Copy the example environment file and fill in your API keys:

# Copy the template (or rename env.example to .env.local)
cp env.example .env.local

Then edit .env.local with your actual API keys:

# OpenRouter API Key (get from https://openrouter.ai/keys)
OPENROUTER_API_KEY=your_openrouter_api_key_here

# Stripe Keys (get from https://dashboard.stripe.com/test/apikeys)
NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=pk_test_your_stripe_publishable_key
STRIPE_SECRET_KEY=sk_test_your_stripe_secret_key

# JWT Secret (generate with: openssl rand -base64 32)
JWT_SECRET=your_jwt_secret_here_min_32_chars

1. Get your API keys:

• OpenRouter: Visit openrouter.ai/keys, sign up, and create an API key
• Stripe: Visit dashboard.stripe.com/test/apikeys and copy your test keys

Development

Start the development server:

npm run dev
# or
yarn dev

How to Use the Demo

Complete A2A Protocol Experience

1. Chat with AI Shopping Agent: Type your vacation preferences naturally

   • Example: "I want a tropical beach vacation with spa treatments"
   • Example: "Looking for an adventure trip in Central America"
   • Example: "Find me a luxury overwater villa experience"

2. Watch A2A Messages: See the Shopping Agent communicate with the Merchant Agent

   • Intent Mandate is created from your request
   • A2A message sent to Merchant Agent with Intent Mandate
   • Merchant Agent responds with signed Cart Mandates (JWT)

3. View Signed Cart Mandates: Browse vacation packages with cryptographic signatures

   • Each package is a Cart Mandate signed by the Merchant
   • Click "View Signature" to see the actual JWT

4. Select Your Package: Choose your preferred vacation

5. Payment Method Selection:

   • Shopping Agent requests payment methods from Credentials Provider via A2A
   • See your available payment methods (from your "wallet")

6. Payment Mandate Creation:

   • User device signs Payment Mandate with JWT
   • Watch the complete mandate chain: Intent → Cart → Payment

7. Stripe Payment: Complete real payment using Stripe test cards

   • Success: 4242 4242 4242 4242
   • Declined: 4000 0000 0000 0002
   • Use any future expiry date and any CVC

8. A2A Message Log: Watch the complete agent communication flow in the sidebar

   • Every agent interaction is logged
   • Full transparency and auditability

9. Confirmation: Receive your booking confirmation with all mandate details!

Learn More About AP2

• Official AP2 Documentation
• AP2 GitHub Repository
• Google Cloud Blog Post

Tech Stack

Core Protocols

• AP2 Protocol - Agent Payments Protocol (Intent, Cart, Payment Mandates)
• A2A Protocol - Agent-to-Agent communication with message parts
• JWT (jose) - Cryptographic signatures for mandates
• W3C Payment Request API - Standard payment flow

AI & Payments

• LangChain - AI agent framework
• OpenRouter - LLM API gateway (Moonshot AI Kimi model)
• Stripe - Payment processing
• SHA-256 - Cryptographic hashing for integrity

Frontend

• Next.js 15 - React framework with Pages Router
• Chakra UI v3 - Beautiful, accessible component library
• TypeScript - Type-safe development
• React 19 - Latest React features

Architecture Overview

Three Agent Architecture (Separate API Endpoints)

1. Shopping Agent (/api/shopping-agent)

   • Orchestrates the entire transaction
   • Communicates with user via chat
   • Sends A2A messages to other agents
   • Creates Intent Mandates and Payment Mandates

2. Merchant Agent (/api/agents/merchant)

   • Receives A2A messages from Shopping Agent
   • Searches product catalog
   • Creates Cart Mandates
   • Signs Cart Mandates with JWT (merchant authorization)

3. Credentials Provider Agent (/api/agents/credentials-provider)

   • Manages user's payment credentials
   • Provides available payment methods via A2A
   • Validates Payment Mandates

AP2 Mandates (Verifiable Digital Credentials)

• IntentMandate - User's purchase intent with expiry
• CartMandate - Merchant-signed cart with JWT authorization
• PaymentMandate - User-signed payment with JWT authorization

Security & Trust

This demo showcases AP2's trust mechanisms:

• Cryptographic signatures on all mandates
• Non-repudiable proof of user intent
• Transparent audit trail of all transactions
• Role-based architecture for privacy

Production Readiness

This is a demo implementation. For production, upgrade JWT from HS256 to RS256 with proper RSA key pairs.

License

This project is MIT licensed. The AP2 reference implementation is Apache 2.0 licensed.

Acknowledgments

• Built on Google's Agent Payments Protocol (AP2)
• Images provided by Unsplash