Hi there!
I was using pam_namespace.so in my multiseat setup to polyinstatiate /tmp and some other paths, so different users won’t collide.
Prior to NixOS 25.11 everything worked fine. However, in 25.11 PAM suddenly started to ignore the /etc/security files. As far as I can see, it now reads /nix/store/…-linux-pam-…/etc/security.
I tried to tackle with this in my spare time and opened an issue: pam_namespace configuration · Issue #504392 · NixOS/nixpkgs · GitHub
Maybe I’m missing something. Does anybody know how to configure PAM modules in NixOS properly? Apparently security.pam.* options are about something else (I can’t configure pam_namespace.so through it as far as I understand).
I would tackle with this issue myself but since this is auth-related and I’m by no means a PAM expert, I would really appreciate the help from people who are 
Thanks!