Using PassportJS, how does one pass additional form fields to the local authentication strategy?

I'm using passportJS and I'm wanting to supply more than just req.body.username and req.body.password to my authentication strategy (passport-local).

I have 3 form fields: username, password, & foo

How do I go about accessing req.body.foo from my local strategy which looks like:

passport.use(new LocalStrategy(
  {usernameField: 'email'},
    function(email, password, done) {
      User.findOne({ email: email }, function(err, user) {
        if (err) { return done(err); }
        if (!user) {
          return done(null, false, { message: 'Unknown user' });
        }
        if (password != 1212) {
          return done(null, false, { message: 'Invalid password' });
        }
        console.log('I just wanna see foo! ) + req.body.foo); // this fails!
        return done(null, user, aToken);

      });
    }
));

I'm calling this inside my route (not as route middleware) like so:

  app.post('/api/auth', function(req, res, next) {
    passport.authenticate('local', {session:false}, function(err, user, token_record) {
      if (err) { return next(err) }
      res.json({access_token:token_record.access_token});
   })(req, res, next);

  });

There's a passReqToCallback option that you can enable, like so:

passport.use(new LocalStrategy(
  {usernameField: 'email', passReqToCallback: true},
  function(req, email, password, done) {
    // now you can check req.body.foo
  }
));

When, set req becomes the first argument to the verify callback, and you can inspect it as you wish.