/lib/live/config/0030-live-debconfig_passwd is in open-infrastructure-system-config 20161101-lts1-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 | #!/bin/sh
## live-config(7) - System Configuration Components
## Copyright (C) 2006-2015 Daniel Baumann <mail@daniel-baumann.ch>
##
## This program comes with ABSOLUTELY NO WARRANTY; for details see COPYING.
## This is free software, and you are welcome to redistribute it
## under certain conditions; see COPYING for details.
#set -e
Cmdline ()
{
	# Reading kernel command line
	for _PARAMETER in ${LIVE_CONFIG_CMDLINE}
	do
		case "${_PARAMETER}" in
			live-config.user-default-groups=*|user-default-groups=*)
				LIVE_USER_DEFAULT_GROUPS="${_PARAMETER#*user-default-groups=}"
				;;
			live-config.user-fullname=*|user-fullname=*)
				LIVE_USER_FULLNAME="${_PARAMETER#*user-fullname=}"
				;;
			live-config.username=*|username=*)
				LIVE_USERNAME="${_PARAMETER#*username=}"
				;;
		esac
	done
}
Init ()
{
	# Checking if package is installed or already configured
	if [ ! -e /var/lib/dpkg/info/live-debconfig.list ] || \
	   [ -e /var/lib/live/config/live-debconfig_passwd ]
	then
		exit 0
	fi
	echo -n " live-debconfig (passwd)"
}
Config ()
{
	# Checking if package is already configured differently
	if grep -q "^${LIVE_USERNAME}:" /etc/passwd
	then
		exit 0
	fi
	# Adjust formating of groups
	if [ -n "${LIVE_USER_DEFAULT_GROUPS}" ]
	then
		LIVE_USER_DEFAULT_GROUPS="$(echo ${LIVE_USER_DEFAULT_GROUPS} | sed -e 's|,| |g')"
	fi
	# Make sure user is not in sudo group if sudo is disabled
	case "${LIVE_CONFIG_NOROOT}" in
		true)
			LIVE_USER_DEFAULT_GROUPS="$(echo ${LIVE_USER_DEFAULT_GROUPS} | sed -e 's|sudo||')"
			;;
	esac
	# Default password is: live
	# passwords can be generated with 'echo "live" | mkpasswd -s',
	# a blank password is 'U6aMy0wojraho'.
	_PASSWORD="8Ab05sVQ4LLps"
cat > /tmp/live-config.cfg << EOF
live-debconfig live-debconfig/passwd/shadow boolean on
#live-debconfig live-debconfig/passwd/root-password password 
#live-debconfig live-debconfig/passwd/root-password-again password 
live-debconfig live-debconfig/passwd/root-password-crypted string *
live-debconfig live-debconfig/passwd/user-name string ${LIVE_USERNAME}
live-debconfig live-debconfig/passwd/user-fullname string ${LIVE_USER_FULLNAME}
#live-debconfig live-debconfig/passwd/user-password password 
#live-debconfig live-debconfig/passwd/user-password-again password 
live-debconfig live-debconfig/passwd/user-password-crypted string ${_PASSWORD}
live-debconfig live-debconfig/passwd/user-home string /home/user
live-debconfig live-debconfig/passwd/user-uid string 1000
live-debconfig live-debconfig/passwd/user-gid string 1000
live-debconfig live-debconfig/passwd/user-default-groups string ${LIVE_USER_DEFAULT_GROUPS}
live-debconfig live-debconfig/passwd/user-system-user boolean false
EOF
	live-debconfig-set-selections /tmp/live-config.cfg
	rm -f /tmp/live-config.cfg
	live-debconfig --debconfig=passwd
	# Creating state file
	touch /var/lib/live/config/live-debconfig_passwd
}
Cmdline
Init
Config
 |