Introduction to Flask-Login

Key Concepts

• User Authentication
• Session Management
• User Loader Function
• Login Required Decorator
• User Roles and Permissions
• Flask-Login Configuration

User Authentication

User authentication is the process of verifying the identity of a user. Flask-Login simplifies this process by providing tools to manage user sessions and handle login and logout operations. It ensures that only authenticated users can access certain parts of your application.

Session Management

Session management involves tracking a user's activity across multiple requests. Flask-Login uses secure cookies to maintain user sessions. When a user logs in, Flask-Login creates a session that persists across requests until the user logs out or the session expires.

User Loader Function

The user loader function is a crucial part of Flask-Login. It retrieves a user object from the database based on the user ID stored in the session. This function is called automatically by Flask-Login to load the user whenever needed.

from flask_login import LoginManager
from models import User

login_manager = LoginManager()
login_manager.init_app(app)

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

Login Required Decorator

The @login_required decorator is used to protect routes that should only be accessible to authenticated users. If a user tries to access a protected route without being logged in, Flask-Login will redirect them to the login page.

from flask_login import login_required

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

User Roles and Permissions

User roles and permissions define what actions a user can perform within the application. Flask-Login does not handle roles and permissions directly, but you can extend it by adding custom methods to your user model. For example, you can define roles like "admin" and "user" and check these roles in your routes.

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

    def is_admin(self):
        return self.role == 'admin'
    

Flask-Login Configuration

Configuring Flask-Login involves setting up the login manager, defining the user loader function, and ensuring that your user model implements the necessary methods. Flask-Login requires your user model to have is_authenticated, is_active, is_anonymous, and get_id methods.

from flask_login import UserMixin

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