When building Python web applications, what are some best practices you follow for ensuring security? Specifically, how do you handle input validation, authentication, and securing sensitive data? Do you prefer using libraries like Flask-Security, Django’s built-in security features, or third-party tools for encryption and authentication?

Additionally, how do you manage session security in Python applications, especially when using tokens like JWT? I'd love to hear about any security measures or tools you’ve found effective for Python-based web development!