@deepfirstsearch/agent-pay-turnkey

Use a key held in Turnkey as an Agent Safe payer: your agent pays x402 APIs in USDC, the key never leaves Turnkey, and every payment stays inside the owner's rules (allowlisted payee, pinned price, sealed plan, on-chain budget).

Beta, unaudited. Not affiliated with Turnkey.

npm install @deepfirstsearch/agent-pay-turnkey @deepfirstsearch/agent-pay @turnkey/sdk-server viem

import { Turnkey } from "@turnkey/sdk-server";
import { createAgentPay, MerchantRegistry } from "@deepfirstsearch/agent-pay";
import { turnkeyPayer } from "@deepfirstsearch/agent-pay-turnkey";

const turnkey = new Turnkey({ apiBaseUrl: "https://api.turnkey.com", apiPublicKey, apiPrivateKey, defaultOrganizationId });
const payer = turnkeyPayer({ client: turnkey.apiClient(), address: "0xYourTurnkeyWalletAddress" });

const pay = createAgentPay({
  registry: new MerchantRegistry([{ origin: "https://api.example.com", payTo: "0x…", network: "eip155:8453", maxPerTx: 50_000n, pricePin: 10_000n }]),
  policy: { allowedNetworks: ["eip155:8453"] },
  payer: () => payer,
  session: { readsUntrustedInput: true, accessesSensitiveData: false, canPay: true },
});

• What Turnkey signs: x402 uses EIP-3009 authorizations, which are EIP-712 typed data. turnkeyPayer hashes the typed data locally with viem and asks Turnkey to sign that exact digest (signRawPayload, HASH_FUNCTION_NO_OP). In our tests, @turnkey/viem 0.14.44's signTypedData recovered to a different address than the signing wallet, while signing the digest recovers correctly; it also makes the signed payload auditable.
• Attacks never reach Turnkey: a 402 with a different payee, a higher price or an unknown origin is refused before any signature is requested, so a prompt-injected agent can't even spend your signing quota on it.
• Only USDC payment authorizations: before anything reaches Turnkey, turnkeyPayer refuses typed data that is not an EIP-3009 TransferWithAuthorization from this wallet on pinned USDC (Base or Base Sepolia, with USDC's own EIP-712 domain), and it refuses messages and transactions.
• What Turnkey's policies can't see: Turnkey receives only a 32-byte digest (HASH_FUNCTION_NO_OP), so a policy that allows ACTIVITY_TYPE_SIGN_RAW_PAYLOAD for this wallet allows any digest: Turnkey can't tell a USDC payment from a Permit or a transaction hash. The check above protects the turnkeyPayer path only. Whoever holds the Turnkey API key can sign anything with this wallet, so keep that key in the payment service, out of the model's process, and give it its own non-root Turnkey user scoped to this one wallet.
• Pair it with on-chain budgets (vaultFunder and the owner CLI in @deepfirstsearch/agent-pay) so a compromised machine still can't exceed what the owner signed.

Develop

npm ci && npm test   # offline tests; set TURNKEY_CREDS=/path/creds.json to also run against a real Turnkey organization