Introduction

Security is a critical aspect of any web application. Flask provides several built-in security features, but implementing custom middleware can add additional layers of protection.

This guide will cover:

  • What middleware is and how it works in Flask
  • Implementing security-focused middleware
  • Logging and monitoring requests
  • Protecting against common threats

Understanding Flask Middleware

Middleware in Flask allows you to intercept and process requests before they reach the view function or after the response is generated. This is useful for:

  • Authentication & Authorization
  • Logging & Monitoring
  • Request Validation
  • Rate Limiting

Creating Custom Middleware in Flask

Flask does not have built-in middleware support like Django, but we can implement it using before_request and after_request hooks.

Implementing Security Middleware

1. Logging Requests for Monitoring

Logging all incoming requests helps in detecting suspicious activity.

from flask import Flask, request
import logging

app = Flask(__name__)
logging.basicConfig(filename="security.log", level=logging.INFO)

@app.before_request
def log_request():
logging.info(f"Request: {request.method} {request.path} from {request.remote_addr}")

@app.route("/")
def home():
return "Welcome to Secure Flask!"

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

2. Implementing API Key Authentication

Restricting access to API endpoints using API keys adds an authentication layer.

API_KEYS = {"secure-key-123"}  # Store securely

@app.before_request
def check_api_key():
api_key = request.headers.get("X-API-KEY")
if api_key not in API_KEYS:
return {"error": "Unauthorized"}, 403

3. Blocking Malicious User Agents

Prevent access from known malicious user agents.

BLOCKED_AGENTS = ["BadBot", "ScraperBot"]

@app.before_request
def block_user_agents():
if request.user_agent.string in BLOCKED_AGENTS:
return {"error": "Forbidden"}, 403

4. Rate Limiting Requests

Prevent abuse by limiting request frequency.

from flask_limiter import Limiter

limiter = Limiter(app, key_func=lambda: request.remote_addr)

@app.route("/secure-endpoint")
@limiter.limit("10 per minute")
def secure_data():
return {"message": "This is rate-limited"}

Conclusion

Implementing custom Flask middleware improves security by logging requests, enforcing authentication, and preventing abuse. Combine middleware with Flask extensions like Flask-Limiter and Flask-Login for enhanced security.

For more Flask security best practices, stay tuned!