You can add basic authorization to the apache folder using .htaccess. If you find munin in /var/www/munin , you can do it this way: edit the file /var/www/munin/.htaccess , put the following content there
AuthType Basic AuthName "Members Only" AuthUserFile /var/www/munin/.htpasswd <limit GET PUT POST> require valid-user </limit>
execute the htpasswd /var/www/munin/.htpasswd admin command to set a password for the admin user
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