Background & Motivation
The GSSAPI (Kerberos) Authentication documentation notes:

Note Kerberos support requires compiling the driver against cyrus-sasl on UNIX-like environments. On Windows, configure the driver to build against the Windows Native SSPI.

This implies that configuration is required to enable building with SSPI.

The current behavior in src/mongoc/CMakeLists.txt is to use SSPI on Windows by default (i.e. if ENABLE_SASL=AUTO).

Scope

• Clarify that Windows uses SSPI by default for Kerberos support.