The default value of umask is 0022 and the default value of path-to-skel is /etc/skel.
The helper is separated from the module to not require direct access from login SELinux domains to the contents of user home directories. The SELinux domain transition happens when the module is executing the mkhomedir_helper.
The helper never touches home directories if they already exist.
Written by Tomas Mraz based on the code originally in pam_mkhomedir module.