Gateway Integration Guide

Turn any FastAPI (or HTTP) service into a MachPay merchant without touching your application code. Per the whitepaper, gateways handle the x402 negotiation and proof-of-solvency checks on your behalf.[file:///Users/abhishektomar/Desktop/git/machpay-docs/whitepaper/machpay_whitepaper.pdf]

The Sidecar Model

Deploy the MachPay Gateway as a sidecar proxy in front of your existing API:

Internet → MachPay Gateway → Your FastAPI app (localhost:8000)

• No SDK rewrites.

• No auth middleware changes.

• The gateway terminates x402, validates signatures, and only forwards authorized requests.

Sample Configuration

config.yaml

target_url: http://localhost:8000
price_per_request: "0.001 USDC"
wallet_private_key: "0xabc123... (keep in env)"
network: base-sepolia
service_id: weather.pro

Best practice: store wallet_private_key in an environment variable and reference it via ${MACHPAY_KEY}.

What the Gateway Does

1. Receives inbound requests and checks for X-MachPay-Auth.

2. If missing, returns 402 Payment Required with the challenge payload.

3. When the agent replays with a valid signature, the gateway:

   • Verifies the EIP-712 intent.

   • Confirms the agent’s bond balance from the latest solvency snapshot.

   • Logs the receipt for the relayer.

   • Forwards the request to your FastAPI backend and streams the response.

This means your service experiences authenticated traffic only, while MachPay handles pricing, accounting, and settlement behind the scenes.[file:///Users/abhishektomar/Desktop/git/machpay-docs/whitepaper/machpay_whitepaper.pdf]