Crate x402 

tempo-x402

HTTP 402 Payment Required for the Tempo blockchain.

Implements pay-per-request API monetization using EIP-712 signed authorizations and TIP-20 (ERC-20 compatible) token transfers on the Tempo chain. One header, one on-chain transfer, zero custodial risk.

How it works

1. Client requests a protected endpoint
2. Server responds 402 with pricing (token, amount, recipient)
3. Client signs an EIP-712 PaymentAuthorization, retries with PAYMENT-SIGNATURE header
4. Facilitator atomically verifies the signature, checks balance/allowance/nonce, and calls transferFrom on-chain
5. Server returns the content + transaction hash

The facilitator holds no user funds — it only has token approval to call transferFrom on behalf of clients who explicitly approved it.

Architecture

Three-party model:

• Client (client::X402Client) — signs payment authorizations, handles the 402 retry flow
• Server (scheme_server::TempoSchemeServer) — gates endpoints, returns 402 with pricing
• Facilitator (scheme_facilitator::TempoSchemeFacilitator) — verifies signatures and settles on-chain

Modules

Module	Purpose
constants	Chain configuration (ID 42431), token address, well-known addresses
eip712	EIP-712 typed-data signing, signature verification, nonce generation
wallet	WASM-compatible wallet: key generation, EIP-712 signing, payment payloads
client	Client SDK — handles 402 flow automatically
scheme	Core trait definitions (scheme::SchemeClient, scheme::SchemeFacilitator, scheme::SchemeServer)
scheme_server	Server implementation: price parsing and payment requirements
scheme_facilitator	Facilitator implementation: signature verification and on-chain settlement
tip20	On-chain TIP-20 token operations (balance, allowance, transfer, approve)
nonce_store	Replay protection backends (in-memory and persistent SQLite)
payment	Payment data structures (payloads, requirements, 402 response body)
response	Facilitator response types (verify/settle results)
hmac	HMAC-SHA256 for facilitator request authentication
security	Constant-time comparison utilities
network	SSRF protection: private IP detection, DNS validation
facilitator_client	HTTP client for calling a remote facilitator
error	Error types for all x402 operations

Quick start

Parse a price and generate payment requirements:

use x402::scheme::SchemeServer;
use x402::scheme_server::TempoSchemeServer;

let server = TempoSchemeServer::default();
let (amount, asset) = server.parse_price("$0.001").unwrap();
assert_eq!(amount, "1000"); // 1000 micro-tokens (6 decimals)

Generate a wallet and sign a payment:

use x402::wallet::{generate_random_key, WalletSigner};

let key = generate_random_key();
let signer = WalletSigner::new(&key).unwrap();
let address = signer.address();

Workspace crates

Crate	Purpose
tempo-x402 (this crate)	Core library
tempo-x402-gateway	API gateway + embedded facilitator
tempo-x402-identity	Agent identity: wallet, faucet, ERC-8004
tempo-x402-soul	Autonomous cognition: plans, memory, coding agent
tempo-x402-node	Self-deploying node with clone orchestration

Feature flags

• full (default) — all features: async runtime, SQLite nonce store, HTTP client
• wasm — WASM-compatible subset: types, EIP-712 signing, wallet (no tokio/rusqlite)
• demo — includes a demo private key for testing

Network

• Chain: Tempo Moderato, Chain ID 42431
• Token: pathUSD 0x20c0000000000000000000000000000000000000 (6 decimals)
• RPC: https://rpc.moderato.tempo.xyz

Re-exports

pub use constants::ChainConfig;

pub use error::X402Error;

pub use scheme_facilitator::TempoSchemeFacilitator;

pub use scheme_server::TempoSchemeServer;

pub use wallet::build_payment_payload;

pub use wallet::generate_random_key;

pub use wallet::recover_message_signer;

pub use wallet::WalletSigner;

Modules

TIP20

Module containing a contract’s types and functions.

client

Client SDK for making paid API requests (handles 402 flow automatically). x402 Client SDK for making paid API requests.

constants

Chain configuration, token addresses, and well-known constants. Chain configuration and well-known constants for the Tempo blockchain.

eip712

EIP-712 typed-data signing, signature verification, and nonce generation. EIP-712 typed-data signing, signature verification, and nonce generation.

error

Error types for x402 operations. Error types for x402 payment operations.

facilitator_client

HTTP client for calling a remote facilitator’s /verify-and-settle endpoint. HTTP client for calling a remote facilitator’s /verify-and-settle endpoint.

hmac

HMAC-SHA256 utilities for authenticating facilitator requests. HMAC-SHA256 utilities for authenticating facilitator requests.

network

Network validation utilities (private IP detection for SSRF protection). Network validation utilities shared across x402 crates.

nonce_store

Replay protection via nonce tracking (in-memory and persistent SQLite backends). Replay protection via nonce tracking.

payment

Payment data structures exchanged between client, server, and facilitator. Payment data structures exchanged between client, server, and facilitator.

response

Facilitator response types returned after verify/settle operations. Facilitator response types for verify and settle operations.

scheme

Core trait definitions for the three-party payment model. Core trait definitions for the three-party payment model.

scheme_facilitator

scheme::SchemeFacilitator implementation: signature verification and on-chain settlement. SchemeFacilitator implementation for the Tempo blockchain.

scheme_server

scheme::SchemeServer implementation: price parsing and payment requirements. SchemeServer implementation for the Tempo blockchain.

security

Constant-time comparison utilities for timing-attack resistance. Shared security utilities for the x402 payment protocol.

tip20

TIP-20 (ERC-20 compatible) on-chain token operations. TIP-20 (ERC-20 compatible) on-chain token operations.

wallet

WASM-compatible wallet: key generation, EIP-712 signing, payment payloads. WASM-compatible wallet for x402 payments.

Structs

PaymentAuthorization