Security roles can be either additive or restrictive, depending on the specific needs of the system and the security model being implemented. However, the choice between these two approaches should be informed by the principles of least privilege and defense in depth. Here’s a breakdown of the two approaches and when they might be used: Additive Approach What It Means: Users start with no access or minimal access, and security roles explicitly grant additional permissions or functionality. When to Use: When you want to ensure strict control over what users can do, minimizing the risk of accidental over-privilege. Systems are designed with a "deny-by-default" philosophy, where permissions are only granted as needed. This is for environments where compliance or sensitive data requires the highest security (e.g., financial and healthcare systems). Advantages: Easier to align with the principle of least privilege, reducing potential attack surfaces. Permissions are explicit and intentional, making it easier to audit and understand. Disadvantages: It can become cumbersome to manage if there are many roles and users with overlapping permissions. Restrictive (Negating) Approach What It Means: Users have a baseline set of permissions or functionality, and security roles restrict or negate specific access. When to Use: Most users require similar baseline functionality, and only a subset needs restricted access (e.g., in public or shared systems). When legacy systems or broad access policies make it challenging to implement a purely additive model. Advantages: Simpler to manage systems with broad default access requirements. Easier to adapt to changes if the baseline access doesn’t frequently change. Disadvantages: This can lead to over-provisioning of permissions if restrictions aren’t carefully defined or enforced. Harder to enforce the least privilege, as the baseline may grant unnecessary permissions. Combination Approach In many cases, a hybrid approach is used: Baseline roles provide minimal or broad permissions needed for general functionality. Additive roles grant specific permissions for specialized tasks or features. Restrictive roles can negate permissions in sensitive areas for specific groups or users. Best Practices Default Deny, Explicit Allow: The safest approach is to start with no permissions and explicitly grant access as needed. Granularity: Use fine-grained permissions to control access to specific features or data. Auditing and Monitoring: Regularly review roles and permissions to ensure they align with business needs and security policies. Role Hierarchy: Consider hierarchical roles where higher-level roles inherit permissions from lower-level ones for ease of management. In general, additive roles align better with modern security best practices, as they provide greater control and reduce the risk of unintended permissions. However, restrictive roles can complement them in certain scenarios, especially in legacy systems or complex environments.