#!/bin/sh

# This script is used on a proxy to refresh the certificates
# from the original servers.
#
# Typical arborescence is :
# /etc/ssl/proxy-certs/www.foobar.com.crt
# /etc/ssl/proxy-certs/www.foobar.com.key
#
# It supports RSA/ECDSA duo :
# /etc/ssl/proxy-certs/www.foobar.com.sigalg-rsa.crt
# /etc/ssl/proxy-certs/www.foobar.com.sigalg-rsa.key
# /etc/ssl/proxy-certs/www.foobar.com.sigalg-ecc.crt
# /etc/ssl/proxy-certs/www.foobar.com.sigalg-ecc.key
# 
# note : don't forget to make the webserver reload the new certificates.

# Stop at the first error
set -e

EXIT_STATUS=0
TMPFILE="$( mktemp )"

for i in *.key; do
	# Filename may be in the form :
	# - www.foobar.com.key
	# - www.foobar.com.sigalg-rsa.key
	# - www.foobar.com.sigalg-ecc.key
	BASENAME="$( echo "$i" | sed 's/\.key$//' )"
	FQDN_HOSTNAME="$( echo "$BASENAME" | sed 's/\.sigalg-.*$//' )"
	SIGALG="$( echo "$BASENAME" | sed -n 's/.*sigalg-\(.*\)$/\1/p' )"  # 'rsa', 'ecc' or ''

	# We don't refresh when there is a certificate request:
	# those are locally served websites
	if [ ! -f "$BASENAME.csr" ] && [ ! -f "$BASENAME.req" ]; then
		# Prepare sigalg/ciphers options
		case "$SIGALG" in
			'ecc')
				SIGALG_OPTIONS="-tls1_2 -cipher ECDSA"
				;;
			'rsa')
				SIGALG_OPTIONS="-tls1_2 -cipher RSA"
				;;
			'')
				SIGALG_OPTIONS=""
				;;
			?)
				echo "ERROR: unknown sigalg." >&2
				EXIT_STATUS=1
				# This may not be critical. We continue, hoping for the best...
				SIGALG_OPTIONS=""
				;;
		esac

		# Fetch the certificate from the origin server and store
		# in a temporary file.
		openssl s_client \
			-showcerts \
			-servername "$FQDN_HOSTNAME" \
			-connect "$FQDN_HOSTNAME:443" $SIGALG_OPTIONS < /dev/null 2>/dev/null | \
		sed -n '/^-----BEGIN CERTIFICATE-----$/,/^-----END CERTIFICATE-----$/p' > "$TMPFILE"

		# Check that the new cert still match the local key
		# (it should also fail safely when the host wasn't reachable)
		if [ "$( openssl x509 -in "$TMPFILE" -pubkey -noout )" != "$( openssl pkey -in "$BASENAME.key" -pubout )" ]; then
			# Mismatch : raise an alert
			echo "WARNING: retrieved certificate does not match '$BASENAME.key'" >&2
			EXIT_STATUS=1
		else
			# Note: we try not to uselessly write and update the files' mtime,
			#       but do it anyway if 'diff' is not available.
			if [ ! -f "$BASENAME.crt" ] || ! which diff >/dev/null || ! diff -q "$BASENAME.crt" "$TMPFILE" >/dev/null ; then
				# Update the local certificate without changing ACL
				cat "$TMPFILE" > "$BASENAME.crt"
			fi
		fi
	fi
done

# While we are at it, let's check the expiry dates
for i in *.crt; do
	if [ "$( date --date="$( openssl x509 -noout -dates -in "$i" | sed -n '/^notAfter/s/^notAfter=//p' )" +%s )" -lt "$(( $( date +%s ) + 86400 ))" ]; then
		echo "WARNING: certificate '$i' near or already expired." >&2
		EXIT_STATUS=1
	fi
done

# Cleanup and exit
rm -f "$TMPFILE"
exit "$EXIT_STATUS"