Product
I use pmwiki
Markdown
As markdown use: Markdown extension
Restrict access
Either you have single admin password (no user name) or you use authuser.php module to allow users.
In config you need to set permissions:
# require valid login before viewing pages
$DefaultPasswords['read'] = 'id:*';
# All admins and Fred and Tom may edit -> only if authuser.php is used!!!
$DefaultPasswords['edit'] = array('@admins', 'id:Fred,Tom');
To hide passwords:
crypt function
crypt pass form