Generating an ECDSA signature

signed_key.ts

/****

Note - This snippet will not be maintained / updated as of Nov 29, 2023. 

Please check out the to generate signers with Neynar https://github.com/neynarxyz/nodejs-sdk

Or you can also use the utility function signKeyRequest inside this package https://github.com/farcasterxyz/hub-monorepo/blob/main/packages/core/src/signers/viemLocalEip712Signer.ts

****/


import { mnemonicToAccount } from "viem/accounts";

/*** EIP-712 helper code ***/

const SIGNED_KEY_REQUEST_VALIDATOR_EIP_712_DOMAIN = {
  name: "Farcaster SignedKeyRequestValidator",
  version: "1",
  chainId: 10,
  verifyingContract: "0x00000000fc700472606ed4fa22623acf62c60553",
} as const;

const SIGNED_KEY_REQUEST_TYPE = [
  { name: "requestFid", type: "uint256" },
  { name: "key", type: "bytes" },
  { name: "deadline", type: "uint256" },
] as const;

const publicKey = ""; // Create and fetch this using the Neynar APIs

/*** Generating a Signed Key Request signature ***/

const appFid = process.env.APP_FID; // Your app's fid
const account = mnemonicToAccount(process.env.APP_MNENOMIC); // Your app's mnemonic

const deadline = Math.floor(Date.now() / 1000) + 86400; // signature is valid for 1 day
const signature = await account.signTypedData({
  domain: SIGNED_KEY_REQUEST_VALIDATOR_EIP_712_DOMAIN,
  types: {
    SignedKeyRequest: SIGNED_KEY_REQUEST_TYPE,
  },
  primaryType: "SignedKeyRequest",
  message: {
    requestFid: BigInt(appFid),
    key: publicKey,
    deadline: BigInt(deadline),
  },
});