I understand what you want to do, but the way you name it is a bit funny. In any case, your logic isn't far off. What you could simply do is include the global.php file along with some other small code, which will result in the page its included in to act as a VBulletin Page, meaning asking for authentication where needed, and keeping the same cookies as the rest of the VBulletin pages.
What you want to accomplish can be done a number of ways, but my best suggestion would be to look up "How to create a VB Powered Page" and that will point you in the right direction:
https://vborg.vbsupport.ru/showthread.php?t=62164