How to Implement User Authentication and Authorization in Flask

1. Introduction

User authentication and authorization are essential features for any web application that involves user accounts and data. User authentication is the process of verifying the identity of a user who tries to access a web application. User authorization is the process of granting or denying access to different resources or functionalities based on the user’s role or permissions.

In this tutorial, you will learn how to implement user authentication and authorization in Flask using Flask-Login, a Flask extension for managing user sessions. Flask-Login provides a convenient way to track the current user in your application and handle common tasks such as logging in, logging out, and remembering users across requests.

By the end of this tutorial, you will be able to create a secure and user-friendly web application with the following features:

• User registration and login forms with validation and error handling
• Password hashing and verification using Werkzeug, a utility library for Flask
• User authentication and session management using Flask-Login
• User authorization and access control using Flask decorators and Flask-Login methods
• Logout and account deletion functionality

To follow this tutorial, you will need a basic understanding of Flask, Python, HTML, and CSS. You will also need to install Flask, Flask-Login, and Werkzeug on your system. You can use pip to install them:

pip install flask
pip install flask-login
pip install werkzeug

Are you ready to create a web application with user authentication and authorization in Flask? Let’s get started!

2. What is Flask-Login?

Flask-Login is a Flask extension that simplifies the implementation of user authentication and authorization in Flask applications. It provides a number of features and benefits that make it easier to manage user sessions and access control.

Some of the features and benefits of Flask-Login are:

• It works with any user model that has an id attribute and supports the methods is_authenticated, is_active, is_anonymous, and get_id.
• It handles the creation and deletion of user sessions using cookies.
• It provides a login_user function that logs a user in and remembers them across requests.
• It provides a logout_user function that logs a user out and clears their session.
• It provides a current_user variable that gives access to the logged-in user object in templates and views.
• It provides a login_required decorator that restricts access to certain views based on the user’s authentication status.
• It provides a user_logged_in and a user_logged_out signal that can be used to perform custom actions when a user logs in or out.
• It supports remember me functionality that allows users to stay logged in even after closing the browser.
• It supports anonymous users that can access public views without logging in.
• It supports custom login views and messages that can be customized according to the application’s needs.

To use Flask-Login, you need to install it using pip:

pip install flask-login

Then, you need to import it and initialize it with your Flask app object:

from flask import Flask
from flask_login import LoginManager

app = Flask(__name__)
login_manager = LoginManager()
login_manager.init_app(app)

Next, you need to define a user loader function that tells Flask-Login how to load a user from the user model. The user loader function takes a user id as an argument and returns the corresponding user object or None if the user does not exist. For example, if you are using SQLAlchemy as your database ORM, you can define the user loader function as follows:

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

Finally, you need to decorate the views that require user authentication with the login_required decorator. This will ensure that only logged-in users can access those views, and redirect anonymous users to the login view. For example, if you have a profile view that shows the user’s information, you can decorate it as follows:

@app.route('/profile')
@login_required
def profile():
    return render_template('profile.html', user=current_user)

As you can see, Flask-Login makes it easy to implement user authentication and authorization in Flask applications. In the next section, you will learn how to set up the project and create the database for your web application.

3. Setting up the Project

In this section, you will learn how to set up the project and create the database for your web application. You will use Flask, a micro web framework for Python, to create the app and SQLAlchemy, a database ORM, to interact with the database. You will also use Flask-Migrate, a Flask extension that integrates SQLAlchemy with Alembic, a database migration tool, to manage the database schema changes.

To set up the project, you will need to do the following steps:

1. Create a virtual environment and activate it.
2. Install the required packages using pip.
3. Create the app folder and the app module.
4. Create the config file and the app factory function.
5. Create the database models and the database instance.
6. Create the migrations folder and the migration scripts.
7. Create the database and apply the migrations.

Let’s go through each step in detail.

1. Create a virtual environment and activate it

A virtual environment is a isolated Python environment that allows you to install packages and run your app without affecting the system Python or other projects. To create a virtual environment, you can use the venv module that comes with Python 3. You can run the following command in your terminal to create a virtual environment named env in your project folder:

python -m venv env

To activate the virtual environment, you can run the following command depending on your operating system:

# On Windows
env\Scripts\activate

# On Linux or Mac
source env/bin/activate

You should see (env) at the beginning of your terminal prompt, indicating that the virtual environment is active. To deactivate the virtual environment, you can run the deactivate command.

2. Install the required packages using pip

Next, you need to install the required packages for your project using pip, the Python package manager. You can use the requirements.txt file to list the packages and their versions that you need. For this project, you will need the following packages:

Flask==1.1.2
Flask-Login==0.5.0
Flask-Migrate==2.7.0
Flask-Script==2.0.6
Flask-WTF==0.14.3
SQLAlchemy==1.4.15
Werkzeug==1.0.1

You can save this file in your project folder and run the following command to install the packages:

pip install -r requirements.txt

This will install the packages and their dependencies in your virtual environment.

3. Create the app folder and the app module

Now, you need to create the app folder and the app module that will contain your application code. You can use the following command to create the app folder:

mkdir app

Then, you need to create the __init__.py file inside the app folder. This file will mark the app folder as a Python package and will contain the app factory function that will create the Flask app object. You can use the following command to create the file:

touch app/__init__.py

You will write the code for the app factory function in the next step.

4. Create the config file and the app factory function

The config file is a Python file that contains the configuration variables for your app, such as the secret key, the database URI, and the debug mode. You can create the config.py file in the app folder and write the following code:

import os

class Config(object):
    # Generate a random secret key using os.urandom(16).hex()
    SECRET_KEY = os.environ.get('SECRET_KEY') or 'a1b2c3d4e5f6g7h8'
    # Use SQLite as the database
    SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL') or 'sqlite:///app.db'
    # Disable the track modifications feature of SQLAlchemy
    SQLALCHEMY_TRACK_MODIFICATIONS = False
    # Enable the debug mode for development
    DEBUG = True

The app factory function is a function that takes a configuration object as an argument and returns a Flask app object with that configuration. You can write the app factory function in the app/__init__.py file as follows:

from flask import Flask
from config import Config

def create_app(config_class=Config):
    # Create the Flask app object
    app = Flask(__name__)
    # Load the configuration from the config object
    app.config.from_object(config_class)
    # Return the app object
    return app

You will add more code to this file in the next steps.

4. Creating the User Model

The user model is a Python class that represents the users of your web application. It defines the attributes and methods of the user objects that will be stored in the database. The user model is also the core component of the user authentication and authorization system, as it interacts with Flask-Login and Werkzeug to handle the user sessions and password hashing.

To create the user model, you will use SQLAlchemy, a database ORM that allows you to write Python code to manipulate the database instead of writing SQL queries. SQLAlchemy provides a declarative way to define the database models using Python classes and decorators. You will also use Flask-Migrate, a Flask extension that integrates SQLAlchemy with Alembic, a database migration tool that allows you to track and apply the changes to the database schema.

To create the user model, you will need to do the following steps:

1. Import the required modules and packages.
2. Create the database instance and the migration instance.
3. Create the user model class and the user loader function.
4. Create the first migration script and apply it to the database.

Let’s go through each step in detail.

1. Import the required modules and packages

First, you need to import the required modules and packages for creating the user model. You can write the following code at the beginning of the app/__init__.py file:

from flask import Flask
from flask_login import LoginManager
from flask_migrate import Migrate
from flask_sqlalchemy import SQLAlchemy
from config import Config

This will import Flask, Flask-Login, Flask-Migrate, SQLAlchemy, and the Config class that you defined in the previous section.

2. Create the database instance and the migration instance

Next, you need to create the database instance and the migration instance that will be used to interact with the database and manage the migrations. You can write the following code after the imports in the app/__init__.py file:

# Create the database instance
db = SQLAlchemy()

# Create the migration instance
migrate = Migrate()

This will create the db and migrate objects that will be initialized with the app object in the app factory function.

3. Create the user model class and the user loader function

Now, you need to create the user model class and the user loader function that will define the user objects and tell Flask-Login how to load them from the database. You can write the following code in a new file named models.py in the app folder:

from app import db, login_manager
from flask_login import UserMixin
from werkzeug.security import generate_password_hash, check_password_hash

# Create the user model class
class User(db.Model, UserMixin):
    # Define the table name
    __tablename__ = 'users'
    # Define the columns
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password_hash = db.Column(db.String(128), nullable=False)

    # Define the representation method
    def __repr__(self):
        return f''

    # Define the method to set the password hash
    def set_password(self, password):
        self.password_hash = generate_password_hash(password)

    # Define the method to check the password hash
    def check_password(self, password):
        return check_password_hash(self.password_hash, password)

# Create the user loader function
@login_manager.user_loader
def load_user(user_id):
    return User.query.get(user_id)

This will create the User class that inherits from db.Model and UserMixin. The db.Model class provides the base class for the database models, and the UserMixin class provides the default implementations of the methods required by Flask-Login, such as is_authenticated, is_active, is_anonymous, and get_id. The User class defines the following attributes and methods:

• __tablename__: The name of the table that will store the user objects in the database.
• id: The primary key column that will store the unique identifier of each user object.
• username: The column that will store the username of each user object. It is unique and not nullable.
• email: The column that will store the email of each user object. It is unique and not nullable.
• password_hash: The column that will store the hashed password of each user object. It is not nullable.
• __repr__: The representation method that will return a string representation of each user object.
• set_password: The method that will take a plain password as an argument and set the password_hash attribute to the hashed value of the password using the generate_password_hash function from Werkzeug.
• check_password: The method that will take a plain password as an argument and return True if it matches the password_hash attribute, or False otherwise, using the check_password_hash function from Werkzeug.

The user loader function is a function that takes a user id as an argument and returns the corresponding user object from the database, or None if the user does not exist. It is decorated with the @login_manager.user_loader decorator that registers it with Flask-Login.

4. Create the first migration script and apply it to the database

Finally, you need to create the first migration script and apply it to the database. A migration script is a file that contains the instructions to create, modify, or delete the tables and columns in the database. Flask-Migrate uses Alembic to generate and apply the migration scripts automatically based on the changes in the database models.

To create the first migration script, you need to run the following command in your terminal:

flask db init
flask db migrate -m "users table"

This will create a migrations folder in your project folder that will contain the configuration and the scripts for the migrations. The flask db init command will initialize the migrations folder, and the flask db migrate command will create the first migration script with the message “users table”. You can inspect the script in the migrations/versions folder and see the code that will create the users table with the columns defined in the User class.

To apply the migration script to the database, you need to run the following command in your terminal:

flask db upgrade

This will execute the migration script and create the users table in the database. You can check the database file app.db in your project folder and see the table and the columns using a database browser tool such as DB Browser for SQLite.

Congratulations! You have successfully created the user model for your web application. In the next section, you will learn how to implement password hashing and verification using Werkzeug.

5. Password Hashing and Verification

Password hashing and verification are important security measures for any web application that involves user passwords. Password hashing is the process of transforming a plain password into a random and irreversible string of characters, called a hash, using a mathematical function, called a hashing algorithm. Password verification is the process of comparing a plain password with a stored hash to check if they match, using the same hashing algorithm.

The main benefits of password hashing and verification are:

• They prevent the exposure of the plain passwords in case of a database breach, as the hashes are difficult to reverse-engineer.
• They protect the users from reusing the same passwords across different websites, as the hashes are unique for each website and each hashing algorithm.
• They allow the users to change their passwords without affecting the stored hashes, as the hashes are generated on the fly for each login attempt.

To implement password hashing and verification in Flask, you will use Werkzeug, a utility library for Flask that provides various tools and functions, including a secure password hashing and verification system. Werkzeug supports multiple hashing algorithms, such as SHA-1, SHA-256, SHA-512, and PBKDF2, and allows you to generate and check password hashes using a simple and consistent interface.

To implement password hashing and verification, you will need to do the following steps:

1. Import the generate_password_hash and check_password_hash functions from Werkzeug.
2. Add the set_password and check_password methods to the User class.
3. Use the set_password method to hash the plain password and store it in the password_hash column.
4. Use the check_password method to verify the plain password against the stored hash.

Let’s go through each step in detail.

1. Import the generate_password_hash and check_password_hash functions from Werkzeug

First, you need to import the generate_password_hash and check_password_hash functions from Werkzeug. These are the functions that will handle the password hashing and verification for you. You can write the following code at the beginning of the app/models.py file:

from werkzeug.security import generate_password_hash, check_password_hash

This will import the functions from the security module of Werkzeug.

2. Add the set_password and check_password methods to the User class

Next, you need to add the set_password and check_password methods to the User class. These are the methods that will use the generate_password_hash and check_password_hash functions to hash and verify the passwords. You can write the following code in the app/models.py file, inside the User class:

# Define the method to set the password hash
def set_password(self, password):
    self.password_hash = generate_password_hash(password)

# Define the method to check the password hash
def check_password(self, password):
    return check_password_hash(self.password_hash, password)

This will define the methods that will take a plain password as an argument and either set or check the password_hash attribute of the user object.

3. Use the set_password method to hash the plain password and store it in the password_hash column

Now, you need to use the set_password method to hash the plain password and store it in the password_hash column. You will do this when you create a new user object or when you update an existing user object. For example, if you have a user registration form that takes the username, email, and password as inputs, you can write the following code to create a new user object and save it to the database:

from app import db
from app.models import User

# Get the form data
username = request.form.get('username')
email = request.form.get('email')
password = request.form.get('password')

# Create a new user object
user = User(username=username, email=email)

# Set the password hash using the set_password method
user.set_password(password)

# Add the user object to the database session
db.session.add(user)

# Commit the changes to the database
db.session.commit()

This will create a new user object with the given username and email, and set the password_hash attribute to the hashed value of the given password using the set_password method. Then, it will add the user object to the database session and commit the changes to the database.

4. Use the check_password method to verify the plain password against the stored hash

Finally, you need to use the check_password method to verify the plain password against the stored hash. You will do this when you authenticate a user who tries to log in to your web application. For example, if you have a user login form that takes the username and password as inputs, you can write the following code to check the credentials and log in the user:

from app import db, login_manager
from app.models import User
from flask_login import login_user

# Get the form data
username = request.form.get('username')
password = request.form.get('password')

# Query the user object by username
user = User.query.filter_by(username=username).first()

# Check if the user exists and the password is correct
if user and user.check_password(password):
    # Log in the user using the login_user function from Flask-Login
    login_user(user)
    # Redirect the user to the home page
    return redirect(url_for('index'))
else:
    # Flash an error message
    flash('Invalid username or password')
    # Redirect the user to the login page
    return redirect(url_for('login'))

This will query the user object by username, and check if the user exists and the password is correct using the check_password method. If the credentials are valid, it will log in the user using the login_user function from Flask-Login, and redirect the user to the home page. If the credentials are invalid, it will flash an error message and redirect the user to the login page.

Congratulations! You have successfully implemented password hashing and verification in Flask using Werkzeug. In the next section, you will learn how to create user registration and login forms using Flask-WTF.

6. User Registration and Login Forms

In this section, you will learn how to create user registration and login forms for your web application. These forms will allow users to create an account, log in with their credentials, and access the protected views of your application.

To create the user registration and login forms, you will use Flask-WTF, a Flask extension that integrates the WTForms library for form validation and rendering. Flask-WTF provides a number of features and benefits that make it easier to work with forms in Flask applications.

Some of the features and benefits of Flask-WTF are:

• It generates HTML forms from Python classes and objects.
• It validates the input data from the forms and handles errors.
• It supports various field types, validators, and widgets.
• It integrates with Bootstrap, a popular CSS framework, for styling the forms.
• It provides a CSRF protection mechanism that prevents cross-site request forgery attacks.

To use Flask-WTF, you need to install it using pip:

pip install flask-wtf

Then, you need to import it and configure it with your Flask app object:

from flask import Flask
from flask_wtf import CSRFProtect

app = Flask(__name__)
app.config['SECRET_KEY'] = 'some-random-string'
csrf = CSRFProtect(app)

The SECRET_KEY configuration is required for Flask-WTF to generate and validate CSRF tokens. You should use a random and secure string for the secret key. The CSRFProtect object enables the CSRF protection for your app.

Next, you need to define the form classes that represent the user registration and login forms. Each form class inherits from the FlaskForm class and defines the fields and validators for the form. For example, you can define the user registration form class as follows:

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import DataRequired, Email, EqualTo, Length

class RegistrationForm(FlaskForm):
    username = StringField('Username', validators=[DataRequired(), Length(min=4, max=20)])
    email = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired(), Length(min=8, max=20)])
    confirm_password = PasswordField('Confirm Password', validators=[DataRequired(), EqualTo('password')])
    submit = SubmitField('Register')

This form class defines four fields: username, email, password, and confirm_password. Each field has a label and a list of validators that check the input data for validity. For example, the username field has a DataRequired validator that ensures that the field is not empty, and a Length validator that ensures that the field is between 4 and 20 characters long. The confirm_password

7. User Authentication and Session Management

In this section, you will learn how to use Flask-Login to handle user authentication and session management in your web application. You will use the login_user and logout_user functions to log users in and out, and the current_user variable to access the logged-in user object. You will also use the login_required decorator to protect the views that require user authentication.

The first step is to import the Flask-Login module and the RegistrationForm and LoginForm classes that you defined in the previous section:

from flask import Flask, render_template, redirect, url_for, flash
from flask_login import LoginManager, login_user, logout_user, current_user, login_required
from forms import RegistrationForm, LoginForm
from models import User

Next, you need to create a login view that renders the login form and handles the user login logic. The login view will check if the user is already logged in, and if so, redirect them to the home page. Otherwise, it will validate the login form and check if the user credentials are correct. If the credentials are correct, it will log the user in using the login_user function and redirect them to the home page. If the credentials are incorrect, it will flash an error message and render the login form again. The login view will also handle the remember me functionality that allows users to stay logged in after closing the browser. For example, you can define the login view as follows:

@app.route('/login', methods=['GET', 'POST'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    form = LoginForm()
    if form.validate_on_submit():
        user = User.query.filter_by(email=form.email.data).first()
        if user and user.check_password(form.password.data):
            login_user(user, remember=form.remember.data)
            return redirect(url_for('home'))
        else:
            flash('Invalid email or password', 'danger')
    return render_template('login.html', form=form)

The login_user function takes a user object and an optional remember argument. The remember argument determines whether the user session will expire when the browser is closed or not. The current_user variable is a proxy object that represents the logged-in user. The is_authenticated attribute returns True if the user is authenticated, and False otherwise.

The next step is to create a logout view that logs the user out and redirects them to the login page. The logout view will use the logout_user function to clear the user session and the current_user variable. For example, you can define the logout view as follows:

@app.route('/logout')
@login_required
def logout():
    logout_user()
    return redirect(url_for('login'))

The logout_user function does not take any arguments. The login_required decorator ensures that only logged-in users can access the logout view, and redirects anonymous users to the login view.

The final step is to use the current_user variable and the login_required decorator to access and protect the views that require user authentication. For example, if you have a profile view that shows the user’s information, you can use the current_user variable to pass the user object to the template, and the login_required decorator to restrict access to the view. For example, you can define the profile view as follows:

@app.route('/profile')
@login_required
def profile():
    return render_template('profile.html', user=current_user)

As you can see, Flask-Login makes it easy to implement user authentication and session management in Flask applications. In the next section, you will learn how to implement user authorization and access control using Flask-Login methods and Flask decorators.

8. User Authorization and Access Control

In this section, you will learn how to implement user authorization and access control in your web application. You will use Flask-Login methods and Flask decorators to restrict access to certain views based on the user’s role or permissions. You will also use Flask-Principal, a Flask extension that provides a flexible and declarative way to manage identity and permissions.

Some of the features and benefits of Flask-Principal are:

• It works with any user model that has an id attribute and supports the methods is_authenticated, is_active, is_anonymous, and get_id.
• It provides a Principal object that stores the identity and permissions of the current user.
• It provides a Permission object that represents a set of required conditions for accessing a resource or functionality.
• It provides a RoleNeed and a UserNeed object that represent the role or user id of the current user.
• It provides a permission_required decorator that restricts access to certain views based on the user’s permissions.
• It provides a identity_loaded signal that can be used to assign roles and permissions to the current user.

To use Flask-Principal, you need to install it using pip:

pip install flask-principal

Then, you need to import it and initialize it with your Flask app object:

from flask import Flask
from flask_principal import Principal

app = Flask(__name__)
principal = Principal(app)

The Principal object enables the identity and permission management for your app.

Next, you need to define the roles and permissions for your web application. For example, you can define two roles: admin and user. The admin role has access to all the views, while the user role has access to only the profile and home views. You can also define a permission for each role using the RoleNeed object and the Permission object. For example, you can define the admin and user permissions as follows:

from flask_principal import RoleNeed, Permission

admin_role = RoleNeed('admin')
user_role = RoleNeed('user')

admin_permission = Permission(admin_role)
user_permission = Permission(user_role)

The RoleNeed object takes a role name as an argument and returns a role object. The Permission object takes one or more role objects as arguments and returns a permission object. The permission object has a method called require that checks if the current user has the required roles for the permission.

The next step is to assign roles and permissions to the current user when they log in. You can use the identity_loaded signal from Flask-Principal to do this. The identity_loaded signal is triggered when a user logs in and the identity of the current user is loaded. You can use the signal to add the roles and permissions of the current user to the Principal object. For example, you can define the identity_loaded function as follows:

from flask_principal import identity_loaded, Identity, RoleNeed, UserNeed

@identity_loaded.connect_via(app)
def on_identity_loaded(sender, identity):
    identity.user = current_user
    if current_user.is_authenticated:
        identity.provides.add(UserNeed(current_user.id))
        if current_user.role == 'admin':
            identity.provides.add(RoleNeed('admin'))
        elif current_user.role == 'user':
            identity.provides.add(RoleNeed('user'))

The identity_loaded function takes a sender and an identity as arguments. The sender is the app object, and the identity is the identity of the current user. The identity object has a provides attribute that stores the roles and permissions of the current user. The function adds the UserNeed and the RoleNeed of the current user to the provides attribute, based on the user’s role attribute. The UserNeed object takes a user id as an argument and returns a user object.

The final step is to use the permission_required decorator from Flask-Principal to protect the views that require user authorization and access control. The permission_required decorator takes a permission object as an argument and restricts access to the view based on the permission. If the current user does not have the required permission, the decorator will raise a 403 Forbidden error. For example, you can use the permission_required decorator to protect the admin view as follows:

@app.route('/admin')
@permission_required(admin_permission)
def admin():
    return render_template('admin.html')

This will ensure that only users with the admin role can access the admin view, and users with the user role or anonymous users will get a 403 Forbidden error.

As you can see, Flask-Principal makes it easy to implement user authorization and access control in Flask applications. In the next section, you will learn how to implement logout and account deletion functionality using Flask-Login and SQLAlchemy.

9. Logout and Account Deletion

In this section, you will learn how to implement logout and account deletion functionality in your web application. You will use Flask-Login and SQLAlchemy to log users out and delete their accounts from the database.

The first step is to import the Flask-Login module and the User model that you defined in the previous sections:

from flask import Flask, render_template, redirect, url_for, flash
from flask_login import LoginManager, login_user, logout_user, current_user, login_required
from models import User

Next, you need to create a logout view that logs the user out and redirects them to the login page. The logout view will use the logout_user function from Flask-Login to clear the user session and the current_user variable. You have already defined this view in the previous section, but here it is again for reference:

@app.route('/logout')
@login_required
def logout():
    logout_user()
    return redirect(url_for('login'))

The logout_user function does not take any arguments. The login_required decorator ensures that only logged-in users can access the logout view, and redirects anonymous users to the login view.

The next step is to create a delete view that deletes the user’s account from the database and redirects them to the login page. The delete view will use the delete method from SQLAlchemy to remove the user object from the database session and commit the changes. The delete view will also use the logout_user function from Flask-Login to log the user out before deleting their account. For example, you can define the delete view as follows:

@app.route('/delete')
@login_required
def delete():
    user = User.query.get(current_user.id)
    logout_user()
    db.session.delete(user)
    db.session.commit()
    flash('Your account has been deleted', 'success')
    return redirect(url_for('login'))

The User.query.get method takes a user id as an argument and returns the corresponding user object or None if the user does not exist. The db.session.delete method takes a user object as an argument and marks it for deletion from the database session. The db.session.commit method commits the changes to the database. The flash function displays a message to the user after the deletion.

As you can see, Flask-Login and SQLAlchemy make it easy to implement logout and account deletion functionality in Flask applications. In the next and final section, you will learn how to write a conclusion for your blog post and summarize the main points of the tutorial.

10. Conclusion

Congratulations! You have successfully completed this tutorial on how to implement user authentication and authorization in Flask using Flask-Login and Flask-Principal. You have learned how to:

• Create a user model with SQLAlchemy and add a role attribute to differentiate between admin and user roles.
• Hash and verify passwords using Werkzeug, a utility library for Flask.
• Create user registration and login forms using Flask-WTF, a Flask extension that integrates the WTForms library.
• Handle user authentication and session management using Flask-Login, a Flask extension that simplifies the implementation of user authentication and authorization.
• Handle user authorization and access control using Flask-Principal, a Flask extension that provides a flexible and declarative way to manage identity and permissions.
• Implement logout and account deletion functionality using Flask-Login and SQLAlchemy.

By following this tutorial, you have gained a solid understanding of the concepts and techniques involved in creating a secure and user-friendly web application with user authentication and authorization in Flask. You have also acquired the skills and knowledge to apply these concepts and techniques to your own Flask projects.

We hope you enjoyed this tutorial and found it useful and informative. If you have any questions, feedback, or suggestions, please feel free to leave a comment below. Thank you for reading and happy coding!