google_api_JWT.js

const credentials = require('./credentials.json');

const googleAuth = require('google-oauth-jwt')
const config = {
  "private_key": credentials.private_key,
  "client_email": credentials.client_email
}
const getToken = () => {
  return new Promise((resolve) => {
    googleAuth.authenticate(
    {
      email: credentials.client_email,
      key: config.private_key,
      scopes: [
        'https://www.googleapis.com/auth/dialogflow'],
    },
    (err, token) => {
      console.log(err)
      resolve(token);
    })
  })
}

console.log("token")
getToken().then((res) => {
  console.log(res)
})

node_server_google_access_token.js

const credentials = require('./credentials.json');
const googleAuth = require('google-oauth-jwt')
const http = require("http");

const host = 'localhost';
const port = 8000;

const getToken = function() {
  return new Promise((resolve, reject) => {
    googleAuth.authenticate({
      email: credentials.client_email,
      key: credentials.private_key,
      scopes: ['https://www.googleapis.com/auth/dialogflow'],
    }, (err, token) => {
      // console.log()
      // console.log("token")
      if (err != null)
        reject(err)
      else
        resolve(token)
    })
  })
}

async function jwtToken(res) {
  var token = await getToken()
  if (res != null) {
    res.end(JSON.stringify({token: token}));
  }
  return token
}

// console.log("got Token - " + jwtToken(null))

const requestListener = function (req, res) {
    res.setHeader("Content-Type", "application/json");
    switch (req.url) {
        case "/token":
            res.writeHead(200);
            jwtToken(res)
            // res.end(JSON.stringify({token: token}));
            break
        default:
            res.writeHead(404);
            res.end(JSON.stringify({error:"Resource not found"}));
    }
}



// getToken().then((res) => {
//   console.log(res)
// })
const server = http.createServer(requestListener);

server.listen(port, host, () => {
    console.log(`Server is running on http://${host}:${port}`);
});

package.json

{
  "name": "@paypalcorp/google_auth",
  "version": "1.0.0",
  "description": "",
  "main": "google_api.js",
  "directories": {
    "test": "test"
  },
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "google-oauth-jwt": "^0.2.0"
  }
}