If subversion on FreeBSD is no longer working with Kerberos auth, change your port config options.
With a recent commit to www/serf, the option for using Kerberos changed.
It was: HEIMDAL_BASE
It is now: GSSAPI_BASE
https://svnweb.freebsd.org/ports/head/www/serf/Makefile?r1=492691&r2=492690&pathrev=492691