I am using PluggableAuth and SimpleSAMLphp. On Wikis upgraded from 1.35.8 to 1.39.2, this works as desired (thanks to a fix from the SimpleSAMLphp discussion page :)
If I deploy a new 1.39.2 wiki, though, I get "Fatal error authenticating user" when signing in with a SAML user. A wiki user with correct attributes is created, and if I navigate away from the error page the user is authenticated and can use the wiki as expected. I see no significant difference between the LocalSettings.php between an upgraded and a newly created wiki.
Is there any way to get more debug information from the PluggableAuth extension?