Understanding guards in NestJS

Guards in NestJS are a key feature used to control access to application routes based on specific conditions, enhancing both security and organization of the code. These guards, which are executed after middleware and before interceptors, can be applied at global, controller, or route levels, allowing for both broad and fine-grained access control. Implemented via classes that adhere to the CanActivate interface, guards use methods like canActivate to determine whether a route should be accessible, often leveraging roles or authorization tokens to make these decisions. Developers can apply multiple guards to a single route, with each guard being executed in sequence; if any guard fails, access is denied. This system supports features like role-based access control using metadata and decorators, as well as the ability to skip certain guards for specific routes when needed.