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You can do it without plugins, you just have to allow subscribers to see Private posts and pages, depending on what you want, so you have to put this code in your functions.php
$subRole = get_role( '...
Although this is not a WP question, it could be done with some PHP/MySQL code. Just the psuedocode:
generate a GUID value on each main page visit
check if the GUID is already in the GUID database