.js

app.get('/services/jwt',(req,res) => {

  const header = {
    "alg": "ES256",
    "typ": "JWT",
    "kid": "yourmapidkey"
  }

  const payload = {
    "iss": "yourteamid",
    "iat": Date.now() / 1000,
    "exp": (Date.now() / 1000) + 15778800,
  }

  var cert = fs.readFileSync('./private.p8'); // the private key you downloaded from Apple Developer Website
  var token = jwt.sign(payload,cert, { header: header } );
  res.json({token: token})
})