Pluggable authentication modules are the core of user authentication in any
modern linux distribution.

Modules pam_passwdqc and pam_ecryptfs were removed between CentOS 6 and CentOS
7, thus making some PAM configuration files no longer valid.

Preupgrade assistant will comment out these modules in your PAM configuration
files after the in-place upgrade automatically, but you should review and
regain the authentication functionality other way, if these modules were
required for your authentication policy.