At first: See also my EDIT below! May be you don't must change the scripts!
The answer of "hotips" is right (+1 for that), but only the links are not longer valid. But you can do the changes in the three scripts by self. It's easy. After installing the perl packages LWP::UserAgent and Crypt::SSLeay (like it was described by "hotips") edit each script and change following lines:
...
my $ua = LWP::UserAgent->new(timeout => 30,
agent => sprintf("munin/%s (libwww-perl/%s)", $Munin::Common::Defaults::MUNIN_VERSION, $LWP::VERSION));
...
...
my $response = $ua->request(HTTP::Request->new('GET',$url));
...
into:
...
my $ua = LWP::UserAgent->new(timeout => 30,
verify_hostname => 0,
agent => sprintf("munin/%s (libwww-perl/%s)", $Munin::Common::Defaults::MUNIN_VERSION, $LWP::VERSION));
...
...
my $response = $ua->get($url);
...
After that don't forget to add the configuration entries env.ports 443
and env.url https://localhost:443/server-status?auto
to /etc/munin/plugin-conf.d/munin-node
(also described by "hotips")
EDIT
Arrghhh! Find out an interesting thing. May be you don't need to change the scripts! In my case after installing the two perl packages and add the configuration entries the scripts working very well with SSL!