Flask Authentication with user login/logout

TL;DR Create a Flask project using virtualenv, install Flask-Login extension, set up a User model with SQLAlchemy, implement login functionality with user registration and logout routes.

Flask Authentication with User Login/Logout

In this article, we'll delve into the world of Flask authentication, specifically focusing on implementing user login and logout functionality in a web application built using Flask.

Why Flask?

Flask is a lightweight Python web framework that provides an efficient way to build robust, scalable applications. Its minimalistic design makes it ideal for building small to medium-sized projects. With its extensive collection of extensions, Flask can be easily extended to support complex functionalities such as user authentication.

Project Setup

To begin with, let's set up a new Flask project using the following command:

mkdir flask_auth
cd flask_auth
virtualenv venv
source venv/bin/activate
pip install flask

Next, create a new file named app.py and add the following code to initialize our Flask application:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return "Welcome to my Flask App!"

if __name__ == "__main__":
    app.run(debug=True)

Flask-Login Extension

To implement user authentication in our Flask application, we'll use the Flask-Login extension. This extension provides a simple way to manage user sessions and authentication.

First, install the Flask-Login extension using pip:

pip install flask-login

Next, initialize the Flask-Login extension in our Flask application:

from flask_login import LoginManager

login_manager = LoginManager()
login_manager.init_app(app)

User Model

To store user information, we'll create a simple User model using SQLAlchemy, which is another popular extension for Flask.

First, install Flask-SQLAlchemy:

pip install flask-sqlalchemy

Next, import the necessary modules and define our User model:

from flask_sqlalchemy import SQLAlchemy

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///users.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    password = db.Column(db.String(120), nullable=False)

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))

Login Functionality

Now that we have our User model in place, let's implement the login functionality. We'll create a new route for user registration and another for user login.

@app.route('/register', methods=['GET', 'POST'])
def register():
    if request.method == 'POST':
        username = request.form.get('username')
        password = request.form.get('password')
        user = User(username=username, password=password)
        db.session.add(user)
        db.session.commit()
        return "User registered successfully!"

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        username = request.form.get('username')
        password = request.form.get('password')
        user = User.query.filter_by(username=username, password=password).first()
        if user:
            login_user(user)
            return "User logged in successfully!"
    return render_template('login.html')

@app.route('/logout')
def logout():
    logout_user()
    return "User logged out successfully!"

Template Integration

To display the registration and login forms, we'll create two new templates named register.html and login.html.

<!-- register.html -->
<form method="POST">
    <input type="text" name="username" placeholder="Username">
    <input type="password" name="password" placeholder="Password">
    <button type="submit">Register</button>
</form>

<!-- login.html -->
<form method="POST">
    <input type="text" name="username" placeholder="Username">
    <input type="password" name="password" placeholder="Password">
    <button type="submit">Login</button>
</form>

Conclusion

In this article, we've successfully implemented user login and logout functionality in a Flask application using the Flask-Login extension. We've also created a simple User model to store user information.

With these basic authentication features in place, you can now focus on building more complex web applications using Flask.

Example Use Cases

• Implementing user roles and permissions
• Integrating with existing authentication systems (e.g., OAuth)
• Creating password reset functionality

Remember to explore the official documentation for Flask-Login and other extensions to unlock their full potential. Happy coding!