It's a legacy MIT Kerberos header that's no longer used by curl since:
355bf01c82 (2015-01-09)
There were still mentions of it after this patch, when using versions
<1.2.3, but those versions aren't supported since:
9918541795 (2008-06-12)
This header remains in use by autotools and cmake to detect MIT Kerberos
(vs. Heimdal, which doesn't have it.)
Ref: https://github.com/curl/curl/pull/18978#issuecomment-3387414995Closes#18990