The evolution of the Internet of Things (IoT) requires a well-defined infrastructure of systems that provides services for device abstraction and data management, and also supports the development of applications. Middleware for IoT has been recognized as the system that can provide these services and has become increasingly important for IoT in recent years. The large amount of data that flows into a middleware system demands a security architecture that ensures the protection of all layers of the system, including the communication channels and border APIs used to integrate the applications and IoT devices. However, this security architecture should be based on lightweight approaches since middleware systems are widely applied in constrained environments. Some works have already defined new solutions and adaptations to existing approaches in order to mitigate IoT middleware security problems. In this sense, this article discusses the role of lightweight approaches to the standardization of a security architecture for IoT middleware systems. This article also analyzes concepts and existing works, and presents some important IoT middleware challenges that may be addressed by emerging lightweight security approaches in order to achieve the consolidation of a standard security architecture and the mitigation of the security problems found in IoT middleware systems.