@nickthelegend69/webrtc-payment-rail-x402

Casper Network x402 payment rail — settles per-segment micropayments through the real CSPR.cloud x402 facilitator using CEP-18 tokens and EIP-712 TransferWithAuthorization signatures.

This is the Casper-specific half of the SDK. It implements the PaymentRail interface from @nickthelegend69/webrtc-payment-sdk-core, turning "charge this viewer 0.15 CSPR" into a signed x402 payload, a facilitator /verify, and an on-chain /settle.

npm install @nickthelegend69/webrtc-payment-rail-x402 @nickthelegend69/webrtc-payment-sdk-core

What it does

consumer.signFn ──▶ buildPayload ──▶ EIP-712 digest + ed25519/secp256k1 sig
                                          │
provider ──▶ rail.verify(payload) ──▶ POST /verify   → { isValid }
provider ──▶ rail.settle(payload) ──▶ POST /settle   → { transaction: txHash }   ← real on-chain tx

• EIP-712 — builds the exact TransferWithAuthorization typed-data the CSPR.cloud facilitator expects (camelCase fields, 33-byte tagged account hashes, bare contract-package hash), via @casper-ecosystem/casper-eip-712.
• Signing — pure-JS ed25519 (@noble/curves) for browser/agent signing, or bring your own signFn (a wallet like CSPR.click).
• Facilitator — wraps /supported, /verify, /settle with the correct authorization: <raw token> header and request body shape.
• Replay-safe — 32-byte nonces; the core SDK rejects reuse before the rail is ever called.

Usage

Provider side (verifies + settles — needs the API key)

import { CasperX402Rail } from "@nickthelegend69/webrtc-payment-rail-x402";

const rail = new CasperX402Rail({
  facilitatorUrl: "https://x402-facilitator.cspr.cloud",
  facilitatorApiKey: process.env.CSPR_CLOUD_API_KEY, // SERVER side only
  network: "casper:casper-test",
  tokenContractHash: process.env.CEP18_TOKEN_CONTRACT!, // 64-hex package hash
  token: { name: "Cep18x402", version: "1", decimals: "9", symbol: "X402" },
  providerAccountHash: process.env.PROVIDER_ACCOUNT_HASH!, // payee
});

⚠️ The facilitator API key is a server-side secret. In a browser app, proxy /verify and /settle through your backend — never ship the key to the client.

Consumer side (only builds + signs — no API key)

import {
  CasperX402Rail,
  makeEd25519SignFn,       // demo/agent signer (raw key)
  createBrowserSigner,     // production wallet signer (e.g. CSPR.click)
} from "@nickthelegend69/webrtc-payment-rail-x402";

const rail = new CasperX402Rail({
  facilitatorUrl: "https://x402-facilitator.cspr.cloud",
  network: "casper:casper-test",
  tokenContractHash: process.env.CEP18_TOKEN_CONTRACT!,
  token: { name: "Cep18x402", version: "1", decimals: "9", symbol: "X402" },
  consumerAccountHash: walletAddress,
  consumerPublicKeyHex: publicKeyHex,
});

// Demo: a real ed25519 hot key (insecure — testnet only)
const signFn = makeEd25519SignFn(process.env.CONSUMER_PRIVATE_KEY!);
// Production: const signFn = createBrowserSigner();  // delegates to the wallet

Then hand rail + signFn to PaywalledRTCConsumer. See the core README.

Config (CasperX402RailConfig)

| Field | Required | Notes | |-------|----------|-------| | facilitatorUrl | ✅ | CSPR.cloud facilitator base URL. | | network | ✅ | "casper:casper-test" or "casper:casper". | | tokenContractHash | ✅ | CEP-18 package hash (any prefix; normalized to bare 64-hex). | | token | ✅ | { name, version, decimals?, symbol? } for the EIP-712 domain. | | facilitatorApiKey | provider | Required to call /verify + /settle. | | providerAccountHash | provider | Payee account hash. | | consumerAccountHash | consumer | Payer account hash. | | consumerPublicKeyHex | consumer | Payer public key (algo-prefixed hex). | | maxTimeoutSeconds | — | Authorization validity window (facilitator min 6). | | resourceUrl | — | Optional resource echoed in the payload. |

Exports

• CasperX402Rail — the PaymentRail implementation.
• FacilitatorClient — thin /supported · /verify · /settle client.
• makeEd25519SignFn, createBrowserSigner, signEd25519, buildTransferDigest — signing helpers.
• buildPaymentPayload, buildWireRequirements, buildExtra — payload builders.
• bareHash, tagged, zeroX, bareNonce, hexToBytes, bytesToHex — Casper hash/format helpers.
• Types: CasperX402RailConfig, CasperNetwork, WireRequirements, FacilitatorVerifyResponse, FacilitatorSettleResponse, BuildPayloadOpts, TransferDigestInput.

EIP-712 shape (the gotcha)

The facilitator is strict. The rail produces exactly:

• primaryType: "TransferWithAuthorization", camelCase fields (validAfter / validBefore).
• from / to as 33-byte tagged account hashes ("0x" + "00" + 64hex).
• contract_package_hash as a bare 64-hex (no prefix, no tag).
• validAfter = now − 600s to absorb clock skew.

If CSPR.cloud changes the schema, Eip712Signer.ts / PayloadBuilder.ts are the only files to touch.

For the full integration walkthrough see docs/USAGE.md.

MIT