The authad plugin has just a on/off for the 'debug' config setting..
With 'debug' config on, it prints just some additional messages at top of the page.
(if you are into php coding, see
https://github.com/splitbrain/dokuwiki/blob/master/lib/plugins/authad/auth.php)
(Sometimes a plugin is using the debug.log (
https://www.dokuwiki.org/devel:debugging), but not the authAD plugin)