What access control model best describes the limitation of a user not being able to use certain features in a system?

The correct answer is a constrained interface because it specifically refers to a design approach that limits user interaction within a system based on predefined parameters. This model is particularly focused on restricting what users can do by presenting them with only certain available options or functionalities.

In situations where a user is unable to access specific features or capabilities of a system, this is typically achieved through a constrained interface which is designed to ensure that users can only engage with a subset of functionalities necessary for their role or tasks. This approach enhances security and usability by guiding users towards appropriate actions while preventing any potential misuse or error that might arise from access to unnecessary or sensitive features.

In contrast, the other access control models, such as role-based access control, identity-based access control, and mandatory access control, pertain more broadly to user permissions based on roles, identities, or system policies, rather than the specific design limitation of available features. These models determine what resources a user can access or actions they can perform, but do not inherently focus on restricting the interface in a way that limits user interaction with system features.