PAM: Enforce a Password-Quality Policy

Harden password quality with pam_pwquality. The config is /etc/security/pwquality.conf (currently all defaults, commented out); your required thresholds are in /root/case/assignment.env.

Set these keys in the config:

• minlen — minimum length (REQ_MINLEN)
• minclass — minimum character classes (REQ_MINCLASS)
• dcredit — minimum required digits, as a negative value (REQ_DCREDIT)

The minimum length and digit count vary per session; every assignment meets the CIS Ubuntu 22.04 Benchmark (length 14 or more, all four character classes). See /root/case/brief.txt.