X402 Facilitator Proxy MCP Server

X402 Facilitator Proxy - Multi-Tenant Payment Gateway

A decentralized, autonomous payment infrastructure for API monetization on Base L2 with programmatic fee routing and agent-compatible settlement protocols.

🏗️ Architecture Overview

The X402 Facilitator Proxy implements a complete multi-tenant payment gateway that enables merchants to monetize APIs through HTTP 402 "Payment Required" responses, while autonomous agents can seamlessly settle transactions using USDC on Base L2.

x402-facilitator-proxy/
├── src/                                    # Core Cloudflare Worker Engine
│   ├── index.ts                           # Main proxy gateway endpoint
│   └── backend/automation/
│       └── sweeper.ts                     # Automated fee collection
├── x402-client-sdk/                       # Core Interface Rails
│   ├── src/
│   │   ├── client-library.ts             # TypeScript SDK
│   │   └── mcp-server.ts                 # Model Context Protocol Server
│   ├── package.json                      # SDK dependencies
│   └── tsconfig.json                     # TypeScript configuration
└── templates/                             # Integration Templates
    ├── express-middleware/
    │   └── x402-guard.js                 # Merchant-Side API Gating
    ├── langchain-ts/
    │   ├── agent.ts                      # TypeScript Agent Template
    │   ├── package.json                  # LangChain dependencies
    │   └── README.md                     # Setup instructions
    └── crewai-python/
        └── agent.py                      # Python Agent Template

🚀 Core Components

1. Cloudflare Worker Proxy Engine

The core backend (src/index.ts) operates as a serverless payment verification gateway deployed on Cloudflare's edge network:

• Endpoint: https://x402-facilitator-proxy.seob5285.workers.dev/api/v1/verify-and-settle
• Platform Vault: 0x2E3DADfb314718849A93c49A78618E586c3b2C60
• Fee Structure: Automated 1% platform fee routing

Key Features:

• Multi-tenant transaction verification
• Base L2 USDC settlement validation
• Automated fee splitting (99% to merchant, 1% to platform)
• Edge-deployed for global low-latency access

2. Model Context Protocol (MCP) Server

The MCP server (x402-client-sdk/src/mcp-server.ts) provides a standardized interface for AI agents to interact with the payment system:

# Start the MCP server locally via stdio
npm run mcp:start

Protocol Features:

• Standard I/O communication interface
• Agent-compatible payment tool registration
• Automatic transaction handling and verification
• Cross-platform AI framework compatibility

3. Merchant-Side API Gating

The Express middleware (templates/express-middleware/x402-guard.js) enables merchants to protect APIs with HTTP 402 challenges:

import { x402TollboothGuard } from './templates/express-middleware/x402-guard.js';

app.use('/api/premium', x402TollboothGuard("0.10", "0xYourWalletAddress"));

Middleware Behavior:

1. Challenge: Returns HTTP 402 with payment instructions when headers are missing
2. Verification: Validates payment through the proxy gateway
3. Access: Grants API access upon successful payment verification

4. Autonomous Agent Templates

TypeScript/LangChain Agent (templates/langchain-ts/agent.ts)

import { createPaymentAgent } from './templates/langchain-ts/agent.js';

const agent = await createPaymentAgent();
const result = await agent.invoke({
  input: JSON.stringify({
    agentPrivateKey: process.env.AGENT_PRIVATE_KEY,
    developerWallet: "0x742d35Cc6297C24aE0E4838C4667C02693C4cB36",
    amountUSD: "0.10"
  })
});

Python/CrewAI Agent (templates/crewai-python/agent.py)

from templates.crewai_python.agent import X402PaymentAgent

agent = X402PaymentAgent()
result = agent.process_payment({
    "agent_private_key": os.getenv("AGENT_PRIVATE_KEY"),
    "developer_wallet": "0x742d35Cc6297C24aE0E4838C4667C02693C4cB36",
    "amount_usd": "0.10"
})

🔧 Quick Start

1. Deploy the Proxy Engine

npm install
npm run deploy

2. Setup the MCP Server

cd x402-client-sdk
npm install
npm run mcp:start

3. Integrate Merchant Middleware

# Copy the Express middleware to your project
cp templates/express-middleware/x402-guard.js your-project/middleware/

# Install in your Express app
import { x402TollboothGuard } from './middleware/x402-guard.js';
app.use('/api/protected', x402TollboothGuard("0.05", "0xYourWallet"));

4. Setup Agent Templates

# For TypeScript/LangChain agents
cd templates/langchain-ts
npm install
npm run dev

# For Python/CrewAI agents
cd templates/crewai-python
pip install -r requirements.txt
python agent.py

🔐 Security & Environment Variables

Critical Security Guidelines

⚠️ NEVER HARDCODE PRIVATE KEYS IN REPOSITORY FILES

All sensitive credentials must be managed through secure environment variables:

Cloudflare Worker Environment (Production)

# Set via Cloudflare Workers dashboard or wrangler
wrangler secret put FACILITATOR_PRIVATE_KEY
wrangler secret put PLATFORM_VAULT_ADDRESS

Local Development Environment

Create .env files for local testing:

# .env (root directory - for Cloudflare Worker development)
FACILITATOR_PRIVATE_KEY=0x1234567890abcdef...
PLATFORM_VAULT_ADDRESS=0x2E3DADfb314718849A93c49A78618E586c3b2C60

# Agent execution environments
AGENT_PRIVATE_KEY=0xabcdef1234567890...
OPENAI_API_KEY=sk-...

Agent Runtime Security

• TypeScript Agents: Use process.env.AGENT_PRIVATE_KEY
• Python Agents: Use os.getenv("AGENT_PRIVATE_KEY")
• MCP Server: Loads keys from system environment at runtime

🌐 Platform Reference

Core Infrastructure

• Verification Gateway: https://x402-facilitator-proxy.seob5285.workers.dev/api/v1/verify-and-settle
• Platform Vault: 0x2E3DADfb314718849A93c49A78618E586c3b2C60
• Network: Base L2 (Chain ID: 8453)
• Payment Token: USDC (0x833589fCD6eDb6E08f4c7C32d4f71b54bda02913)

Fee Structure

• Merchant Revenue: 99% of payment amount
• Platform Fee: 1% automatically routed to platform vault
• Gas Optimization: Batched transfers for cost efficiency

📖 Integration Patterns

HTTP 402 Payment Flow

1. API Request: Client attempts to access protected endpoint
2. Payment Challenge: Server responds with HTTP 402 and payment instructions
3. Agent Processing: Autonomous agent detects 402, executes USDC payment split
4. Verification: Proxy gateway validates on-chain transaction
5. Access Granted: Original API request succeeds with payment headers

Agent Integration Workflow

graph TD
    A[Agent API Call] --> B{HTTP 402?}
    B -->|Yes| C[Parse Payment Requirements]
    C --> D[Execute USDC Split Transfer]
    D --> E[Submit to Proxy Gateway]
    E --> F[Retry Original Request]
    F --> G[Access Granted]
    B -->|No| G

🛠️ Development Commands

# Core proxy development
npm run dev              # Start local development server
npm run deploy           # Deploy to Cloudflare Workers
npm run cf-typegen       # Generate Cloudflare types

# SDK development
cd x402-client-sdk
npm run build           # Build TypeScript SDK
npm run mcp:start       # Start MCP server

# Template testing
cd templates/langchain-ts
npm run dev            # Test TypeScript agent

cd templates/crewai-python
python agent.py        # Test Python agent

# Automated fee collection
npm run sweep          # Execute fee sweeping automation

📚 Documentation

• Client Integration Guide: Detailed integration instructions
• LangChain Template README: TypeScript agent setup
• API Reference: Core gateway endpoints and responses

🤝 Contributing

1. Fork the repository
2. Create feature branches for new integrations
3. Test against Base L2 testnet before mainnet deployment
4. Submit pull requests with comprehensive test coverage

📄 License

This project is licensed under the MIT License - enabling open-source innovation while maintaining platform sustainability through programmatic fee routing.

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Built for the autonomous economy. Powered by Base L2. Secured by multi-tenant verification.