Use for questions having to do with the Security Support Provider Interface (SSPI) API.
The Security Support Provider Interface (sspi) is a Microsoft Windows API used to perform security-related operations such as authentication. It is implemented as a a dynamic-link library (DLL) supplied with the operating system. SSPI is the means by which the operating system loads SSPs (Security Support Providers), such as Kerberos and NTLM, when the system boots. The SSPI is the implementation of the Generic Security Service API (gssapi) in Windows.
This article, while dated, is a good primer on sspi: Logon and Authentication Technologies
