Flask-Login extension - Mini Project: Build & Apply

User Login System with Flask-Login Extension

📖 Scenario: You are building a simple web app where users can log in and see a welcome page. To manage user sessions easily, you will use the Flask-Login extension.

🎯 Goal: Create a Flask app that uses Flask-Login to handle user login, logout, and session management with a single test user.

📋 What You'll Learn

Create a Flask app instance

Set up Flask-Login with a user loader

Create a User class compatible with Flask-Login

Implement login and logout routes

Protect a route so only logged-in users can access it

💡 Why This Matters

🌍 Real World

User login systems are essential for websites and apps to control access and personalize content.

💼 Career

Understanding Flask-Login helps backend developers build secure user authentication in Python web apps.

1

Set up Flask app and User class

Import Flask from flask and LoginManager, UserMixin from flask_login. Create a Flask app called app. Define a User class that inherits from UserMixin and has an id attribute set to 1.

Flask

# Your code here

Need a hint?

Start by importing Flask and LoginManager. Then create the app and a simple User class with an id.

2

Configure Flask-Login and user loader

Create a LoginManager instance called login_manager and initialize it with app. Define a function load_user that takes user_id and returns a User instance if user_id is '1', else returns None. Register this function with login_manager.user_loader.

Flask

from flask import Flask
from flask_login import LoginManager, UserMixin

app = Flask(__name__)

class User(UserMixin):
    def __init__(self):
        self.id = 1

# Your code here

Need a hint?

Initialize LoginManager with your app and create a user loader function that returns the User instance for id '1'.

3

Add login and logout routes

Import login_user, logout_user, and login_required from flask_login. Create a route /login that logs in the User instance and returns the text 'Logged in!'. Create a route /logout that logs out the user and returns 'Logged out!'.

Flask

from flask import Flask
from flask_login import LoginManager, UserMixin, login_user, logout_user, login_required

app = Flask(__name__)

class User(UserMixin):
    def __init__(self):
        self.id = 1

login_manager = LoginManager()
login_manager.init_app(app)

@login_manager.user_loader
def load_user(user_id):
    if user_id == '1':
        return User()
    return None

# Your code here

Need a hint?

Create routes for login and logout that call the right Flask-Login functions and return simple text.

4

Protect a route with login_required

Create a route /profile that is protected with @login_required. This route should return the text 'Welcome to your profile!'. Also, set app.secret_key to 'secret123' to enable session management.

Flask

from flask import Flask
from flask_login import LoginManager, UserMixin, login_user, logout_user, login_required

app = Flask(__name__)

class User(UserMixin):
    def __init__(self):
        self.id = 1

login_manager = LoginManager()
login_manager.init_app(app)

@login_manager.user_loader
def load_user(user_id):
    if user_id == '1':
        return User()
    return None

@app.route('/login')
def login():
    user = User()
    login_user(user)
    return 'Logged in!'

@app.route('/logout')
def logout():
    logout_user()
    return 'Logged out!'

# Your code here

Need a hint?

Set a secret key for sessions and protect the profile route with @login_required decorator.