x402 Explained: HTTP‑Native Micropayments for AI Agents (With Real Code)

说明与用途

在 FastAPI 中实现了最小化的 x402 服务器，使自主代理能够通过 HTTP 标头自动协商、支付并检索资源。

问题

Autonomous agents need a way to pay for services without human‑in‑the‑loop approvals.

结果

Implemented a minimal x402 server in FastAPI that protects an endpoint, challenges clients with 402, verifies on‑chain USDC payments, and serves the resource upon successful proof.

工作流

• 1. Client sends normal GET request to resource.
• 2. Server responds 402 with Payment-Request header containing price, address, nonce, etc.
• 3. Client decodes header, creates payment proof (tx hash, signature) and sends it in Payment header on retry.
• 4. Server verifies proof against nonce and payment details; if valid returns 200 with payload, else 402.
• 5. Client consumes payload; no further round‑trip needed unless nonce rotated.

证据

The protocol is stateless on the server side beyond the nonce

来源

Below is a self‑contained example that you can drop into a main.py file and run with uvicorn main:app

来源