PAM is an authn core in any modern mainstream Linux distro. If you build and/or tweak Linux boxes, PAM was almost always here right with you. The only question is do you know what exacly PAM do?
I remember when I was in school (about 15 years ago) Slackware was one of the few distro's that didn't have PAM and they made a big point of it. So I did a quick Google just now and found that this year (2020) even Slackware got PAM [1]. Had a good chuckle over that.
[1] https://alien.slackbook.org/blog/slackware-introduces-pam-in...