Script to create and add a signer to a Farcaster account. https://dololand.com/add-farcaster-signer

add-signer.ts

/**
 * Add a signer to your Farcaster account.
 *
 * Requirements:
 * - Farcaster account (FID) already registered
 * - Wallet must control the FID
 * - Wallet must have ETH on Optimism for gas
 *
 * .env file:
 * WALLET_MNEMONIC="your twelve word seed phrase"
 * WALLET_FID=1234
 */

import * as ed from '@noble/ed25519';
import {
	bytesToHex,
	createPublicClient,
	createWalletClient,
	encodeAbiParameters,
	http,
} from 'viem';
import { mnemonicToAccount } from 'viem/accounts';
import { optimism } from 'viem/chains';
import {
	KEY_GATEWAY_ADDRESS,
	keyGatewayABI,
	SIGNED_KEY_REQUEST_VALIDATOR_EIP_712_TYPES,
	signedKeyRequestValidatorABI,
} from '@farcaster/core';

// Load the wallet and FID from environment variables
const account = mnemonicToAccount(process.env.WALLET_MNEMONIC!);
const fid = Number(process.env.WALLET_FID);

console.log('Account Address:', account.address);
console.log('Account FID:', fid);

// Generate a new Ed25519 keypair to use as a signer
const privateKey = ed.utils.randomPrivateKey();
const signerKeypair = {
	privateKey: bytesToHex(privateKey),
	publicKey: bytesToHex(await ed.getPublicKeyAsync(privateKey)),
};

console.log('Signer Public Key:', signerKeypair.publicKey);
console.log('Signer Private Key:', signerKeypair.privateKey);

// Set a deadline (24 hours from now) for the key authorization to be valid
const deadline = BigInt(Math.floor(Date.now() / 1000) + 86400);

// Construct and sign the EIP-712 typed data payload for authorizing the signer
const keyRequestData = {
	...SIGNED_KEY_REQUEST_VALIDATOR_EIP_712_TYPES,
	primaryType: 'SignedKeyRequest',
	message: {
		requestFid: BigInt(fid),
		key: signerKeypair.publicKey,
		deadline,
	},
} as const;

const signature = await account.signTypedData(keyRequestData);
console.log('Signed Key Request:', signature);

// Encode the signed key request into ABI-encoded metadata for the contract
const metadata = encodeAbiParameters(signedKeyRequestValidatorABI[12].inputs, [
	{
		requestFid: BigInt(fid),
		requestSigner: account.address,
		signature,
		deadline,
	},
]);

// Create a read-only client to simulate the transaction
const publicClient = createPublicClient({
	chain: optimism,
	transport: http(),
});

// Simulate the `add` call to prepare the transaction for submission
const { request } = await publicClient.simulateContract({
	account,
	address: KEY_GATEWAY_ADDRESS,
	abi: keyGatewayABI,
	functionName: 'add',
	args: [1, signerKeypair.publicKey, 1, metadata],
});

console.log(request);

// Create a wallet client to send the actual transaction
const walletClient = createWalletClient({
	chain: optimism,
	transport: http(),
});

// Submit the transaction to register the signer onchain
const txn = await walletClient.writeContract(request);
console.log(`Transaction: https://optimistic.etherscan.io/tx/${txn}`);