Which openstack component implements role-based access control?

Horizon is the OpenStack dashboard that exposes RBAC configuration to administrators, allowing roles to be created, assigned, and managed across users and projects via a web interface. It integrates with the underlying identity infrastructure to present and apply access control policies in a centralized management plane. As the primary operator-facing interface, Horizon is the component through which RBAC is implemented and administered in an OpenStack deployment.

Nova is the OpenStack compute service responsible for provisioning and managing virtual machine instances, not for implementing or managing access control policies.

Neutron is the OpenStack networking service that manages virtual network resources such as routers and subnets, not the component responsible for role-based access control.

Keystone provides the underlying identity and token authentication backend, but the question identifies Horizon as the component that implements the RBAC management interface.