MongoDB, a leading NoSQL database, is widely utilized in Node.js applications and multi-tenant architectures, where Role-Based Access Control (RBAC) is crucial for managing user access to resources. While MongoDB's built-in RBAC manages access at the database level, it lacks application-level authorization, necessitating external solutions like Permit.io for defining roles and permissions at the application layer. This guide details implementing multi-tenant RBAC using MongoDB, Mongoose, and Permit.io, focusing on a customer support platform as a case study. In this system, users can belong to multiple tenants with distinct roles, such as Admin, Agent, and Customer, each with specific permissions for managing or accessing support tickets. The article emphasizes the importance of separating authorization logic from database queries, using Permit.io to centralize role and permission management, and employing PDP-Level Filtering to ensure users only access allowed data. It explores the practicalities of defining data models, creating tenants, assigning roles, and implementing permission checks, ultimately enhancing security, scalability, and flexibility in managing multi-tenant environments.