Authorization as a Service (AaaS) offers developers a way to manage user access and permissions in applications without building these systems from scratch, emphasizing the complexity and importance of authorization in modern applications. It distinguishes authorization from authentication by focusing on access control once a user's identity is verified. AaaS allows developers to outsource authorization management to specialized providers, enhancing security, saving time, and reducing the risk of vulnerabilities by leveraging expert-built solutions. It supports complex authorization models like Attribute-based and Relationship-based access control. The build vs. buy debate in authorization is increasingly leaning towards utilizing external services due to their security expertise and compliance features. The document discusses criteria for selecting an AaaS provider, such as compatibility, scalability, and ease of use, and provides examples of policy-as-code and graph-based solutions like Open Policy Agent, AWS Cedar, Google Zanzibar, and SpiceDB. These solutions help streamline the deployment and management of authorization policies, making them accessible to non-developers through user-friendly interfaces, ultimately allowing developers to focus on core application functionalities.