1. Introduction

In this tutorial, we aim to guide you through the process of securing your Flask application using HTTPS. HTTPS is a protocol that encrypts the data transferred between the user's browser and the server, safeguarding any sensitive data from possible interception.

By the end of this tutorial, you will be able to:
- Understand the importance of HTTPS and its role in web application security.
- Set up HTTPS for your Flask application.

Before beginning, you should have a basic understanding of:
- Python programming language
- Flask web framework
- Basic understanding of web protocols (HTTP/HTTPS)

2. Step-by-Step Guide

HTTPS is not implemented directly in Flask. Instead, we will be using an HTTP server that supports HTTPS, such as Nginx, and a WSGI application server, like Gunicorn, to serve our Flask application.

2.1. Installing Necessary Tools

First, let's install Nginx and Gunicorn:

sudo apt-get update
sudo apt-get install nginx
pip install gunicorn

2.2. Configuring Nginx

Next, we need to configure Nginx to forward requests to Gunicorn. Create a new configuration file in /etc/nginx/sites-available/:

sudo nano /etc/nginx/sites-available/myflaskapp

In the newly created file, add the following configuration:

server {
    listen 80;
    server_name your_domain_or_IP;

    location / {
        include proxy_params;
        proxy_pass http://unix:/tmp/myflaskapp.sock;
    }
}

Then, enable this configuration by linking it to the sites-enabled directory and restarting Nginx:

sudo ln -s /etc/nginx/sites-available/myflaskapp /etc/nginx/sites-enabled
sudo systemctl restart nginx

2.3. Obtaining a SSL Certificate

To enable HTTPS, we need an SSL certificate. Let's use Let's Encrypt, a free and open certificate authority. We can install it using the Certbot tool:

sudo add-apt-repository ppa:certbot/certbot
sudo apt-get update
sudo apt-get install python-certbot-nginx

To obtain and install a certificate:

sudo certbot --nginx -d your_domain_or_IP

3. Code Examples

Let's assume we have a simple Flask application:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello, Secure World!"

if __name__ == '__main__':
    app.run()

Now, let's serve this application using Gunicorn:

gunicorn --bind unix:/tmp/myflaskapp.sock myflaskapp:app

Here, myflaskapp is the name of your Python script, and app is the Flask instance.

This will create a Unix socket at /tmp/myflaskapp.sock, and Nginx will forward all requests to this socket.

4. Summary

In this tutorial, we walked through the process of securing a Flask application with HTTPS. We used Nginx as the HTTP server, Gunicorn to serve the Flask application, and Let's Encrypt to obtain a free SSL certificate.

Next, you might want to learn about advanced Flask topics, like using Flask extensions, or securing your application further with user authentication and role-based access control.

5. Practice Exercises

1. Set up HTTPS for a different Flask application.
2. Research and implement HTTP Strict Transport Security (HSTS) in your Nginx configuration.
3. Learn more about SSL/TLS and explain why it's crucial for data security.

Remember to apply what you've learned in a practical context. Happy coding!