Protecting routes with auth middleware in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of auth middleware in Express?

Auth middleware checks if a user is logged in before allowing access to certain routes. It protects routes from unauthorized users.

beginner

How do you apply auth middleware to a specific route in Express?

You add the middleware function as a second argument in the route definition, like: app.get('/dashboard', authMiddleware, (req, res) => {...}).

beginner

What should auth middleware do if the user is not authenticated?

It should stop the request and respond with a status like 401 Unauthorized or redirect the user to a login page.

intermediate

Why is middleware a good way to protect routes?

Middleware lets you reuse the same auth check on many routes without repeating code. It keeps your code clean and organized.

beginner

Show a simple example of auth middleware in Express.

A simple auth middleware checks if <code>req.user</code> exists. If yes, it calls <code>next()</code> to continue. If no, it sends a 401 response.<br><br><code>function authMiddleware(req, res, next) {<br>  if (req.user) {<br>    next();<br>  } else {<br>    res.status(401).send('Unauthorized');<br>  }<br>}</code>

What does auth middleware typically check before allowing access to a route?

A If the user is logged in

B If the server is running

C If the database is connected

D If the route exists

Auth middleware checks if the user is logged in or authenticated before allowing access.

How do you add middleware to protect a route in Express?

A Call it inside the route handler

B Add it as a second argument in the route definition

C Add it after the route handler

D Middleware cannot protect routes

Middleware is added as a second argument before the route handler to protect the route.

What should auth middleware do if the user is not authenticated?

A Log the user in automatically

B Call next() to continue

C Ignore the request

D Send a 401 Unauthorized response

If the user is not authenticated, middleware should stop the request and send a 401 Unauthorized response.

Why is using middleware good for protecting many routes?

A It repeats code for each route

B It slows down the server

C It keeps code clean and reusable

D It only works for one route

Middleware allows reusing the same auth logic on many routes, keeping code clean.

Which Express method is used to continue to the next middleware or route handler?

A next()

B res.send()

C app.use()

D req.next()

Calling next() passes control to the next middleware or route handler.

Explain how auth middleware protects routes in Express and why it is useful.

Think about how middleware acts like a gatekeeper before route handlers.

Write a simple auth middleware function for Express and describe what it does.

Focus on the basic structure and the decision to allow or block access.