Added a plugin to check SSL certificate expiry times

This plugin connects to remote hosts and checks the HTTPS certificate
expiry time.

Example: https://munin.buddycloud.com/ssl-day.html

plugins/ssl_certificates/ssl_

@@ -0,0 +1,53 @@
+#!/bin/bash
+# -*- sh -*-
+
+: << =cut
+
+=head1 NAME
+
+ssl_ - Plugin to monitor certificate expiration
+
+=head1 CONFIGURATION
+
+This plugin does not normally require configuration.
+
+To set warning and critical levels do like this:
+
+  [ssl_*]
+      env.warning 30:
+
+=head1 AUTHOR
+
+Pactrick Domack
+
+Copyright (C) 2013 Patrick Domack <patrickdk@patrickdk.com>
+
+=head1 LICENSE
+
+=cut
+
+. $MUNIN_LIBDIR/plugins/plugin.sh
+
+SITE=${0##*ssl_}
+
+case $1 in
+    config)
+
+        echo "graph_title $SITE SSL Certificate Expire"
+        echo 'graph_args --base 1000'
+        echo 'graph_vlabel days left'
+        echo 'graph_category ssl'
+        echo "graph_info This graph shows the days left for the certificate being served by $SITE"
+        echo 'expire.label days'
+        print_warning expire
+        print_critical expire
+
+        exit 0
+        ;;
+esac
+
+cert=$(echo "" | openssl s_client -CApath /etc/ssl/certs -connect "${SITE}:443" 2>/dev/null);
+
+if [[ "${cert}" = *"-----BEGIN CERTIFICATE-----"* ]]; then
+  echo "${cert}" | openssl x509 -noout -enddate | awk -F= 'BEGIN { split("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec", month, " "); for (i=1; i<=12; i++) mdigit[month[i]] = i; } /notAfter/ { split($0,a,"="); split(a[2],b," "); split(b[3],time,":"); datetime=b[4] " " mdigit[b[1]] " " b[2] " " time[1] " " time[2] " " time[3]; days=(mktime(datetime)-systime())/86400; print "expire.value " days; }'
+fi