express_passport_link_compatible.js

app.get('/auth/facebook', (req, res, next) => {
    passport.authenticate('facebook', {
        callbackURL: 'http://localhost:3000/auth/facebook/callback?' + 
          (req.query.redirect_uri ? '&redirect_uri=' + req.query.redirect_uri : '') +
          (req.query.account_linking_token ? '&account_linking_token=' + req.query.account_linking_token : ''),
        scope: ['public_profile', 'email', 'user_friends', 'user_likes']
    })(req, res, next);
});

app.get('/auth/callback/facebook', (req, res, next) => {
    passport.authenticate('facebook', {
        callbackURL: 'http://localhost:3000/auth/facebook/callback?' + 
          (req.query.redirect_uri ? '&redirect_uri=' + req.query.redirect_uri : '') +
          (req.query.account_linking_token ? '&account_linking_token=' + req.query.account_linking_token : ''),
        scope: ['public_profile', 'email', 'user_friends', 'user_likes']
    })(req, res, next);
  }, (req, res) => {
    // Successful authentication - link the accounts and redirect.
    botly.getPSID(req.query.account_linking_token, (err, body) => {
        //You should handle errors
        var PSID = body.recipient;  
        req.user.update({PSID: req.user}, (err, data) => {
            //link done, let's redirect
            res.redirect(req.query.redirect_uri + '&authorization_code=' + req.user.id);
        });
    });
});