It seems like PHP-SAML is no longer including the xmlseclibs source code in their releases (https://github.com/onelogin/php-saml/archive/refs/tags/3.4.1.tar.gz). These files are missing from /var/www/html/functions/ with the 1.5.2 version of the container.

This breaks SAML2 authentication. It can be fixed by manually downloading xmlseclibs (https://github.com/robrichards/xmlseclibs) and mounting it into the container. These files require the all users read and execute permissions as well or PHP will throw an error.

This seems like a temporary fix though, and also seems like it isn't intended behavior when you build the phpIPAM container.