✍️ How to sign with MetaMask and verify with Node.js using ethers.js

sign.tsx

import { useState } from "react"
import { ethers } from "ethers"

export default function Sign() {
  const [isVerified, setIsVerified] = useState(false)

  const onClick = async () => {
    if (!window.ethereum) {
      console.error('!window.ethereum')
      return
    }

    const provider = new ethers.providers.Web3Provider(window.ethereum)
    await provider.send('eth_requestAccounts', [])

    const signer = await provider.getSigner()
    const message = 'message'
    const address = await signer.getAddress()
    const signature = await signer.signMessage(message)
    const response = await fetch('/api/verify', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json; charset=UTF-8',
      },
      body: JSON.stringify({ message, address, signature }),
    })

    const body = await response.json()
    setIsVerified(body.isVerified)
  }

  return (
    <>
      <button onClick={onClick}>Sign</button>
      {isVerified && <p>Verified!</p>}
    </>
  )
}

verify.ts

import { ethers } from "ethers"

export default async function apiVerify (req, res) {
  const {message, address: expected, signature} = req.body
  const digest = ethers.utils.hashMessage(message)
  const actual = ethers.utils.recoverAddress(digest, signature)
  const isVerified = actual === expected

  res.send({isVerified})
}