A versatile authentication server or service (VAS) is a single authentication product or service supporting user authentication in multiplatform environments (on-premises and in the cloud). It may be delivered as server software, a virtual or hardware appliance, or a cloud-based service. In addition to the VAS vendor’s own and OEMed proprietary methods, if any, a VAS must support either open authentication methods or third-party proprietary authentication methods, without the need for separate third-party authentication servers or services.