nginx: generate certificates for test targets

Podman will be used to test the generated Debian packages to ensure that
they work properly. However, this means that it is NOT shione and
therefore cannot solve letsencrypt challenge among many other things
that can only be done by shione. The goal is to have a staging area that
can mock the latter.

debian/nginx-config.postinst

@@ -2,21 +2,31 @@
 #
 # TODO: Handle "$1".
 
-set -e
+set -eu
 
 #DEBHELPER#
 
 # `certbot` *must* be installed by this package.
+if [ "$(hostname)" = shione ]; then
 	certbot \
-	--nginx \
 		--agree-tos \
-	--redirect \
-	--hsts \
-	--staple-ocsp \
 		--email renken+letsencrypt@shione.net \
 		-d shione.net \
 		-d www.shione.net \
 		-d git.shione.net
+else
+	out=/etc/letsencrypt/live/shione.net
+
+	mkdir -p -- "$out"
+	openssl genrsa \
+		>"$out"/privkey.pem
+	openssl req \
+		-new \
+		-x509 \
+		-key /etc/letsencrypt/live/shione.net/privkey.pem \
+		-subj '/CN=shione.net/O=shione.net./C=FR' \
+		>/etc/letsencrypt/live/shione.net/fullchain.pem
+fi
 
 # Apply new nginx configuration.
 deb-systemd-invoke restart nginx