all: use drop-ins replacement for configuring ssh server

Using this method give more flexibility to user that need to build
image with custom SSH server configuration.

2 files changed, 121 insertions, 5 deletions

diff --git a/build-arch-gce b/build-arch-gce
index 81b938a..a1db33c 100755
--- a/build-arch-gce
+++ b/build-arch-gce
@@ -110,6 +110,10 @@ echo '-- Configuring journald.'
 mkdir -p $mount_dir/etc/systemd/journald.conf.d
 cp ./sys/etc/systemd/journald.conf.d/00-google.conf $mount_dir/etc/systemd/journald.conf.d/
 
+## Disable password authentication and root login on SSH server.
+echo '-- Configuring ssh.'
+cp ./sys/etc/ssh/sshd_config $mount_dir/etc/ssh/
+
 arch-chroot -- "$mount_dir" /bin/bash -s <<-'EOS'
 	set -eEuo pipefail
 	trap 'echo "Error: \`$BASH_COMMAND\` exited with status $?"' ERR
@@ -121,11 +125,7 @@ arch-chroot -- "$mount_dir" /bin/bash -s <<-'EOS'
 	echo '-- Running locale-gen.'
 	locale-gen
 
-	echo '-- Configuring ssh.'
-	gawk -i assert -i inplace '
-		/^#PasswordAuthentication / { $0 = "PasswordAuthentication no"; ++f1 }
-		/^#PermitRootLogin / { $0 = "PermitRootLogin no"; ++f2 }
-		{ print } END { assert(f1 * f2 == 1, "f == 1") }' /etc/ssh/sshd_config
+	echo '-- Enabling sshd service.'
 	systemctl --quiet enable sshd.service
 
 	echo '-- Configuring pacman.'
diff --git a/sys/etc/ssh/sshd_config b/sys/etc/ssh/sshd_config
new file mode 100644
index 0000000..ad7e1f2
--- /dev/null
+++ b/sys/etc/ssh/sshd_config
@@ -0,0 +1,116 @@
+#	$OpenBSD: sshd_config,v 1.104 2021/07/02 05:11:21 dtucker Exp $
+
+# This is the sshd server system-wide configuration file.  See
+# sshd_config(5) for more information.
+
+# This sshd was compiled with PATH=/usr/local/sbin:/usr/local/bin:/usr/bin
+
+# The strategy used for options in the default sshd_config shipped with
+# OpenSSH is to specify options with their default value where
+# possible, but leave them commented.  Uncommented options override the
+# default value.
+
+#Port 22
+#AddressFamily any
+#ListenAddress 0.0.0.0
+#ListenAddress ::
+
+#HostKey /etc/ssh/ssh_host_rsa_key
+#HostKey /etc/ssh/ssh_host_ecdsa_key
+#HostKey /etc/ssh/ssh_host_ed25519_key
+
+# Ciphers and keying
+#RekeyLimit default none
+
+# Logging
+#SyslogFacility AUTH
+#LogLevel INFO
+
+# Authentication:
+
+#LoginGraceTime 2m
+PermitRootLogin no
+#StrictModes yes
+#MaxAuthTries 6
+#MaxSessions 10
+
+#PubkeyAuthentication yes
+
+# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
+# but this is overridden so installations will only check .ssh/authorized_keys
+AuthorizedKeysFile	.ssh/authorized_keys
+
+#AuthorizedPrincipalsFile none
+
+#AuthorizedKeysCommand none
+#AuthorizedKeysCommandUser nobody
+
+# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
+#HostbasedAuthentication no
+# Change to yes if you don't trust ~/.ssh/known_hosts for
+# HostbasedAuthentication
+#IgnoreUserKnownHosts no
+# Don't read the user's ~/.rhosts and ~/.shosts files
+#IgnoreRhosts yes
+
+# To disable tunneled clear text passwords, change to no here!
+PasswordAuthentication no
+#PermitEmptyPasswords no
+
+# Change to no to disable s/key passwords
+KbdInteractiveAuthentication no
+
+# Kerberos options
+#KerberosAuthentication no
+#KerberosOrLocalPasswd yes
+#KerberosTicketCleanup yes
+#KerberosGetAFSToken no
+
+# GSSAPI options
+#GSSAPIAuthentication no
+#GSSAPICleanupCredentials yes
+
+# Set this to 'yes' to enable PAM authentication, account processing,
+# and session processing. If this is enabled, PAM authentication will
+# be allowed through the KbdInteractiveAuthentication and
+# PasswordAuthentication.  Depending on your PAM configuration,
+# PAM authentication via KbdInteractiveAuthentication may bypass
+# the setting of "PermitRootLogin without-password".
+# If you just want the PAM account and session checks to run without
+# PAM authentication, then enable this but set PasswordAuthentication
+# and KbdInteractiveAuthentication to 'no'.
+UsePAM yes
+
+#AllowAgentForwarding yes
+#AllowTcpForwarding yes
+#GatewayPorts no
+#X11Forwarding no
+#X11DisplayOffset 10
+#X11UseLocalhost yes
+#PermitTTY yes
+PrintMotd no # pam does that
+#PrintLastLog yes
+#TCPKeepAlive yes
+#PermitUserEnvironment no
+#Compression delayed
+#ClientAliveInterval 0
+#ClientAliveCountMax 3
+#UseDNS no
+#PidFile /run/sshd.pid
+#MaxStartups 10:30:100
+#PermitTunnel no
+#ChrootDirectory none
+#VersionAddendum none
+
+# no default banner path
+#Banner none
+
+# override default of no subsystems
+Subsystem	sftp	/usr/lib/ssh/sftp-server
+
+# Example of overriding settings on a per-user basis
+#Match User anoncvs
+#	X11Forwarding no
+#	AllowTcpForwarding no
+#	PermitTTY no
+#	ForceCommand cvs server