For anyone that comes across this post, I figured out what happened and why this stopped
working.
Early on when deploying FreeIPA and building the AD trust, I had figured out by nesting AD
group via ext_group into idM local Admin group and then creating ID View overrides for
said AD accounts ( no need to specify any specific posix user override values) it would
pass kerberos (kbtgt) auth via auth header when using the IPA API from the CLI.
During some clean-up I had removed those ID View user overrides; thus creating my own
issue. :-(
Re-creating the ID View override entries for the AD users fixed the issue. You can also
see the successful 200 POST from the AD user in /var/log/httpd/access_log