Some code confusing in MEAN Web Development 2en

exports.signin = function(req, res, next) {
    passport.authenticate('local', function(err, user, info) {
        if (err || !user) {
            res.status(400).send(info);
        } else {
            // Remove sensitive data before user.password = undefined; user.salt = undefined;
            req.login(user, function(err) {
                if (err) {
                    res.status(400).send(err);
                } else {
                    res.json(user);
                }
            });
        }
    })(req, res, next);
};

This a piece of code in the "MEAN Web Development" book by AmosQ.Haviv.Who could tell me what the method passport.authenticate()'tail:(req, res, next) means?Is that a Closure?

via leonardodavinci