The Security Support Provider Interface (SSPI) is an application programming interface (API) that applications should use to request security services from security service providers. In Windows 2000, a security support provider is a dynamic link library that supports the SSPI specification and that provides one or more security support packages. Each security support package (SSP) supports one specific security protocol and implements the SSPI functions according to that security protocol.
Applications can use the services of a security package in various ways. Applications can use the SSPI functions directly or through higher-level protocols or APIs, such as RPC, DCOM, WinSock, or WinInet. Nevertheless, one way or another, access to the security services is always through the SSPI layer.
SSPI defines four interface categories for credential management, context management, message exchange, and package management. Note that SSPI does not provide any interfaces for sending and receiving messages.