In the transition from Role-Based Access Control (RBAC) to Fine-Grained Authorization (FGA) using WorkOS, the focus shifts from assigning broad roles to tailoring access based on multiple factors like role, seniority, location, and time, thus enhancing security. FGA allows for more detailed access rules, determining not just whether a user can access a resource but which specific data they can view or edit. The process involves defining resource types, relationships, and inheritance rules to create a robust authorization model. WorkOS facilitates the implementation of this model through a schema language and API, enabling consistent enforcement across various applications and microservices. Testing and validating the access model is crucial, and this is achieved through test assertions and automated scripts. The guide outlines the steps to design and test the FGA model, highlighting its advantages over traditional RBAC by addressing its limitations like role explosion and lack of flexibility, and sets the stage for integrating these advanced access controls into applications.