Developing secure Nest.js applications can be enhanced through the integration of Role-Based Access Control (RBAC) using Permit.io, an authorization-as-a-service provider. This guide walks through setting up a Nest.js project and integrating it with Permit.io to safeguard API endpoints, ensuring only authorized users can access them. It begins with installing the Nest.js CLI and creating a new project, followed by incorporating the popular Passport library for authentication. A Nest.js Decorator Guard is then created to manage authorization logic, initially hardcoded but later integrated with Permit.io's policy management. Permit.io's dashboard facilitates setting up roles and policies, such as an Admin role with access to protected resources, with the ability to dynamically check permissions using the Permit SDK in the guard. By implementing this setup, developers can effectively manage user permissions, demonstrating how changing user roles impacts access to protected routes, thereby enhancing the security and control of application endpoints.