talk/plugins/talk-plugin-facebook-auth/server/passport.js

const FacebookStrategy = require('passport-facebook').Strategy;
const UsersService = require('services/users');
const {ValidateUserLogin} = require('services/passport');
let {
  ROOT_URL
} = require('config');

if (ROOT_URL[ROOT_URL.length - 1] !== '/') {
  ROOT_URL += '/';
}

module.exports = (passport) => {
  if (process.env.TALK_FACEBOOK_APP_ID && process.env.TALK_FACEBOOK_APP_SECRET && process.env.TALK_ROOT_URL) {
    passport.use(new FacebookStrategy({
      clientID: process.env.TALK_FACEBOOK_APP_ID,
      clientSecret: process.env.TALK_FACEBOOK_APP_SECRET,
      callbackURL: `${ROOT_URL}api/v1/auth/facebook/callback`,
      passReqToCallback: true,
      profileFields: ['id', 'displayName', 'picture.type(large)']
    }, async (req, accessToken, refreshToken, profile, done) => {

      let user;
      try {
        user = await UsersService.findOrCreateExternalUser(profile);
      } catch (err) {
        return done(err);
      }

      return ValidateUserLogin(profile, user, done);
    }));
  } else if (process.env.NODE_ENV !== 'test') {
    throw new Error('Facebook cannot be enabled, missing one of TALK_FACEBOOK_APP_ID, TALK_FACEBOOK_APP_SECRET, TALK_ROOT_URL');
  }
};