Login_required decorator in Flask - Mini Project: Build & Apply

Login_required decorator

📖 Scenario: You are building a simple Flask web app that has some pages only accessible to logged-in users.To protect these pages, you want to create a login_required decorator that checks if a user is logged in before allowing access.

🎯 Goal: Create a login_required decorator in Flask that redirects users to the login page if they are not logged in.Use this decorator on a protected route to ensure only logged-in users can see it.

📋 What You'll Learn

Create a Flask app with a route /dashboard that requires login

Create a login_required decorator that checks if session['logged_in'] is true

If not logged in, redirect to /login

Use the decorator on the /dashboard route

💡 Why This Matters

🌍 Real World

Web apps often need to restrict access to certain pages only to logged-in users. This decorator pattern helps keep code clean and reusable.

💼 Career

Understanding how to protect routes and manage user sessions is a key skill for backend web developers working with Flask or similar frameworks.

1

Set up Flask app and session

Import Flask and create an app instance called app. Set a secret key 'secret123' for sessions.

Flask

from flask import Flask, session, redirect, url_for

app = Flask(__name__)
app.secret_key = 'secret123'
# Your code here

Need a hint?

Remember to import Flask and create the app variable.

2

Create the login_required decorator

Define a function called login_required that takes a function f as argument. Inside, define a wrapper function decorated_function that checks if session.get('logged_in') is true. If not, return redirect(url_for('login')). Otherwise, return f(). Use functools.wraps(f) to preserve function metadata. Return decorated_function from login_required.

Flask

from flask import Flask, session, redirect, url_for
import functools

app = Flask(__name__)
app.secret_key = 'secret123'

# Define login_required decorator here
# Your code here

Need a hint?

Use functools.wraps and check session.get('logged_in').

3

Create the protected dashboard route

Create a route /dashboard using @app.route('/dashboard'). Define a function dashboard decorated with @login_required. Return the string 'Welcome to your dashboard!' from this function.

Flask

from flask import Flask, session, redirect, url_for
import functools

app = Flask(__name__)
app.secret_key = 'secret123'

def login_required(f):
    @functools.wraps(f)
    def decorated_function(*args, **kwargs):
        if not session.get('logged_in'):
            return redirect(url_for('login'))
        return f(*args, **kwargs)
    return decorated_function

# Create /dashboard route with @login_required
# Your code here

Need a hint?

Use @app.route('/dashboard') and decorate with @login_required.

4

Add a simple login route to set session

Create a route /login using @app.route('/login'). Define a function login that sets session['logged_in'] = True and returns the string 'You are now logged in.'.

Flask

from flask import Flask, session, redirect, url_for
import functools

app = Flask(__name__)
app.secret_key = 'secret123'

def login_required(f):
    @functools.wraps(f)
    def decorated_function(*args, **kwargs):
        if not session.get('logged_in'):
            return redirect(url_for('login'))
        return f(*args, **kwargs)
    return decorated_function

@app.route('/dashboard')
@login_required
def dashboard():
    return 'Welcome to your dashboard!'

# Create /login route to set session['logged_in'] = True
# Your code here

Need a hint?

Create a simple login route that sets session['logged_in'] to True.