x402 Facilitator Proxy

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](CLIENT_INTEGRATION.md): Detailed integration instructions
• [LangChain Template README](templates/langchain-ts/README.md): TypeScript agent setup
• [API Reference](src/index.ts): 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.