an example script to show how to sign a Celo transaction

signTx.js

const Web3 = require("web3")
const ContractKit = require('@celo/contractkit')
const web3 = new Web3('https://forno.celo.org')
const kit = ContractKit.newKitFromWeb3(web3)

let anAddress = '0xD86518b29BB52a5DAC5991eACf09481CE4B0710d'

async function signTx(){

  let goldtoken = await kit.contracts.getGoldToken()
  let gasContract = await kit.contracts.getGasPriceMinimum()
  let gas = await gasContract.getGasPriceMinimum(goldtoken.address))
  let gasPrice = gas * 1.5 // gasPrice buffer to ensure it gets included in the next block
  
  kit.addAccount(account.privateKey) // your account private key

  let tx = {
    to: anAddress,
    from: account.address,  // the account associated with your private key
    data: '',               // input the appropriate encoded transaction data
    gas: 500000,            // estimate gas for your tx
    gasPrice: gasPrice,
    value: '',              // amount of CELO to send in the tx
    chainId: 42220,         // Celo mainnet chainId
    nonce: 1                // lookup the nonce for the account
  }

  let wallet = kit.getWallet()
  let signedTx = await wallet.signTransaction(tx)

  console.log(signedTx)
}

signTx()