Before_request as middleware alternative in Flask - Mini Project: Build & Apply

Using before_request as Middleware Alternative in Flask

📖 Scenario: You are building a simple Flask web app that needs to check if a user is authenticated before allowing access to certain pages.Instead of writing the authentication check inside every route, you want to use Flask's before_request function as a middleware alternative to run this check automatically before each request.

🎯 Goal: Create a Flask app that uses before_request to check if a user is logged in before accessing the /dashboard route. If the user is not logged in, redirect them to the /login page.

📋 What You'll Learn

Create a Flask app instance named app

Define a global variable logged_in set to False initially

Use @app.before_request to create a function named check_login that checks if the user is logged in

If the user is not logged in and tries to access /dashboard, redirect to /login

Create two routes: /login and /dashboard that return simple text responses

💡 Why This Matters

🌍 Real World

Web apps often need to check user authentication before allowing access to certain pages. Using before_request as middleware helps keep the code clean and centralized.

💼 Career

Understanding middleware patterns and request lifecycle in Flask is essential for backend web development roles.

1

Set up Flask app and login status

Import Flask and redirect from flask. Create a Flask app instance called app. Create a global variable called logged_in and set it to False.

Flask

from flask import Flask, redirect

# Your code here

Need a hint?

Use app = Flask(__name__) to create the app instance.

Set logged_in = False to represent the user not logged in yet.

2

Add before_request function to check login

Use the @app.before_request decorator to create a function named check_login. Inside it, check if logged_in is False and if the requested path is /dashboard. If both are true, return a redirect to /login.

Flask

from flask import Flask, redirect, request

app = Flask(__name__)

logged_in = False

# Add before_request function to check login
# Your code here

Need a hint?

Use @app.before_request to run check_login before every request.

Use request.path to get the current URL path.

3

Create /login and /dashboard routes

Create a route /login that returns the text 'Please log in.'. Create another route /dashboard that returns the text 'Welcome to your dashboard.'.

Flask

from flask import Flask, redirect, request

app = Flask(__name__)

logged_in = False

@app.before_request
def check_login():
    if not logged_in and request.path == '/dashboard':
        return redirect('/login')

# Add /login and /dashboard routes
# Your code here

Need a hint?

Use @app.route('/login') and @app.route('/dashboard') to define routes.

Return simple strings from each route function.

4

Add app run block for local testing

Add the standard Flask app run block: if __name__ == '__main__': and inside it call app.run(debug=True).

Flask

from flask import Flask, redirect, request

app = Flask(__name__)

logged_in = False

@app.before_request
def check_login():
    if not logged_in and request.path == '/dashboard':
        return redirect('/login')

@app.route('/login')
def login():
    return 'Please log in.'

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

# Add app run block
# Your code here

Need a hint?

This block allows you to run the Flask app locally for testing.