create kumod user during rpm and deb install

I haven't tested the deb stuff explicitly, will see what
happens when it makes it through CI

assets/build-deb.sh

@@ -34,6 +34,15 @@ EOF
 
 ./assets/install.sh pkg/debian/opt/kumomta
 
+cat > pkg/debian/preinst <<EOF
+#!/bin/sh
+getent group kumod >/dev/null || groupadd --system kumod
+getent passwd kumod >/dev/null || \
+    useradd --system -g kumod -d /var/spool/kumod -s /sbin/nologin \
+    -c "Service account for kumomta" kumod
+exit 0
+EOF
+
 deps=$(cd pkg && dpkg-shlibdeps -O -e debian/opt/kumomta/*bin/*)
 mv pkg/debian/control pkg/debian/DEBIAN/control
 sed -i '/^Source:/d' pkg/debian/DEBIAN/control  # The `Source:` field needs to be valid in a binary package

assets/build-rpm.sh

@@ -27,6 +27,7 @@ Packager: Wez Furlong <wez@wezfurlong.org>
 License: MIT
 URL: https://kumomta.com
 Summary: A high performance, modern MTA.
+Requires(pre): shadow-utils
 
 %description
 A high performance, modern MTA.
@@ -34,6 +35,13 @@ A high performance, modern MTA.
 %build
 echo "Doing the build bit here"
 
+%pre
+getent group kumod >/dev/null || groupadd --system kumod
+getent passwd kumod >/dev/null || \
+    useradd --system -g kumod -d /var/spool/kumod -s /sbin/nologin \
+    -c "Service account for kumomta" kumod
+exit 0
+
 %install
 set -x
 cd ${HERE}