The built-in mypage's document library by default lists the childrens of /Root/Profiles/username/Document_Library.
The easiest way to achieve this is if you add a new List portlet to the 'My page' and bind it to the 'shared' folder. But this way you cannot list multiple shared folders in one list.
Steps to achieve this:
- Copy /Root/Profiles/(apps)/UserProfile/Browse into to the chosen user profiles (/Root/Profiles/username/(apps)/UserProfile/Browse. This way the users that should work on the shared folder would have a custom 'My page' with the shared folder as a list
- Navigate to the newly created Browse pages and switch to edit mode
- Add a 'List' portlet to one of the zones
- Open the portlet actions (top-right corner of the portlet) and click on 'Edit' to open the portlet property dialog.
- There're tons of things on this dialog to set, but the three that you have to set is the ViewFrame on the 'Content List' tab (set is to: /Root/System/SystemPlugins/ListView/ViewFrame.ascx) and the Bind Target + Custom root path on the Contenxt binding tab (Bind target should be Custom root and add your shared folders path into the Custom root path)
The steps above should be made on all the userprofiles that are related. Another solution could be if you change the built-in profile Browse page (/Root/Profiles/(apps)/UserProfile/Browse). This way the shared folder will be displayed on every users 'My page' but the users who aren't allow to see the items of the shared folder will see an empty list.
To get all the 'shared' document/folder/content items you have to use the permission queries but they are only available through the OData or c# API, so you have to create a custom grid/collection view to achieve this.