Authentication middleware in web applications is a function that intercepts requests to manage access control by validating tokens and permissions, allowing developers to focus on business logic rather than duplicating authentication checks across routes. Modern frameworks support middleware functions that can run logic before or after requests reach the application's core handlers. This blog explains how to implement authentication middleware using Node.js and Python, showcasing tools like Descope that streamline the process with SDKs and decorators for token validation and role checks. Descope's tools enable centralized management of authentication, improving maintainability by offloading session validation. Python decorators provide a way to wrap additional behavior around functions, making them useful for building authentication middleware in frameworks like Flask, FastAPI, or Django. Descope offers prebuilt decorators for session validation and role enforcement, simplifying security and enhancing user experience across web applications.