https://joshwright.com/tips/facebook-authentication-for-nodejs/

facebook-auth-routes.js

import app from 'src/api';
import * as qs from 'query-string';
import axios from 'axios';

const settings = {
  appId: '**************',
  appSecret: '**************************',
  redirectUrl: 'https://myapp.com/facebook/callback',
};

app.get('/facebook/login', async (req, res) => {
  const params = qs.stringify({
    client_id: settings.appId,
    redirect_uri: settings.redirectUrl,
    scope: ['email'].join(','),
    response_type: 'code',
    auth_type: 'rerequest',
  });

  const url = `https://www.facebook.com/v4.0/dialog/oauth?${params}`;
  res.redirect(url);
});

app.get('/facebook/callback', async (req, res) => {
  // Get the login code
  const { code } = req.query;

  // Fetch the access token
  const tokenResponse = await axios({
    url: 'https://graph.facebook.com/v4.0/oauth/access_token',
    method: 'get',
    params: {
      client_id: settings.appId,
      client_secret: settings.appSecret,
      redirect_uri: settings.redirectUrl,
      code,
    },
  });
  const { access_token } = tokenResponse.data;

  // Fetch the email
  const meResponse = await axios({
    url: 'https://graph.facebook.com/me',
    method: 'get',
    params: {
      fields: ['email'].join(','), // matches scope
      access_token,
    },
  });
  const { email } = meResponse.data;

  // TODO: login with email

  res.redirect('/');
});