A Cloud Access Security Broker (CASB) is a security technology that is designed to provide visibility, compliance, and control over cloud-based services and applications. It acts as a middleman between users and cloud services, enabling organizations to enforce security policies, monitor activity, and detect and prevent threats in the cloud. CASBs can be used to manage user access and permissions, including those granted to third-party OAuth applications, to ensure that they are appropriate and compliant with company policies.