passport-local-mongoose Error Messages

I would like to get the passport-local-mongoose specific error message after a failed login attempt. Are they connect-flash messages? I have tried this

app.post('/login', function(req, res, next) {
  passport.authenticate('local', function(err, user, info) {
    if (err) { return res.send(info); }
    if (!user) { return res.send(info); }
    req.logIn(user, function(err) {
      if (err) { return res.send(info); }
      return res.send(user.username);
    });
  })(req, res, next);
});

But then I will get passportJS error messages like "Missing credentials". I would like to get the incorrectPasswordError or incorrectUsernameError, just returned in plain json. I use client side templating, so redirection is made on the client. How can I access the error messages?