The Security Support Provider Interface (SSPI) model provides a single interface through which a client-server transport application can use any of the various security packages available on a computer or network. SSPI allows an application to use a security package even though it does not "understand" the underlying security protocols of the package. SSPI is also flexible enough to allow more sophisticated security-aware applications to take advantage of the capabilities of a particular security package.
To use a security package, both the client and server components of a transport application can call the LoadLibrary function to load SECURITY.DLL. The client and server then use the GetProcAddress function to get a pointer to the InitSecurityInterface function, which returns a pointer to a SecurityFunctionTable dispatch table. The table contains pointers to the security provider's implementations of the various SSPI functions.