I would like some help understanding the following example from the passport.js authenticate documentation:
app.get('/login', function(req, res, next) {
passport.authenticate('local', function(err, user, info) {
if (err) { return next(err); }
if (!user) { return res.redirect('/login'); }
req.logIn(user, function(err) {
if (err) { return next(err); }
return res.redirect('/users/' + user.username);
});
})(req, res, next); //***UNSURE ABOUT THIS***
});
I understand what the code does - but I don't know what the (req, res, next)at the end of the callback function is for. Why is it necessary? Does it provide the values for (err, user, info)? If that's the case, why don't I see more function calls ending with arguments - Is it perhaps something to do with passing on the next object?
Would love for someone to help me improve my understanding of this concept.
Request handlers are Express middleware; they get a request, a response, and a way to pass on execution to the next layer of middleware. passport.authenticate returns middleware, but it hasn’t been attached with app.use(), so you have to pass the appropriate arguments manually.
The fact that the callback from passport.authenticate also has three arguments is just a coincidence. They won’t have the same values.