SharePoint Online Document Authorization Filter

Is it possible to implement a custom Authorization Filter when a user attempts to access a document in SharePoint  Online.   I have an external data store that I would like to evaluate to determine if a user should have access to a document.  If the user should not have access the user will not be able to view the document.  

I am trying to determine if there is an alternate approach to setting add-hoc permissions on certain documents for certain users.