__uacme_obtain: allow RENEW_HOOK to be specified from stdin.

type/__uacme_obtain/man.rst

@@ -39,6 +39,7 @@ install-key-to
 
 renew-hook
   Renew hook executed on certificate renewal (e.g. `service nginx reload`).
+  If this is '-', then the type's standard input will be used instead.
 
 force-cert-ownership-to
   Override default ownership for TLS certificate, passed as argument to chown.

type/__uacme_obtain/manifest

@@ -109,8 +109,12 @@ export CERT_TARGET
 RENEW_HOOK=
 if [ -f "${__object:?}/parameter/renew-hook" ];
 then
+	if [ "$(cat "${__object:?}/parameter/renew-hook")" = "-" ]; then
+		RENEW_HOOK="$(cat "${__object:?}/stdin")"
+	else
 		RENEW_HOOK="$(cat "${__object:?}/parameter/renew-hook")"
 	fi
+fi
 export RENEW_HOOK
 
 if [ -n "$KEY_TARGET" ] && [ -z "$CERT_TARGET" ]; then