/etc/pam.d/i3lock is in i3lock 2.8-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | #
# PAM configuration file for the i3lock screen locker. By default, it includes
# the 'login' configuration file (see /etc/pam.d/login)
#
auth include login
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