Standardised behaviour for links to attachments users do not have access to

Issue Summary

At the moment, there are multiple ways where Confluence users can link to attachments from one page to another. 

1. A user can copy the full URL of the attachment and save that as a link on a different page. 
2. A user can add a link to an attachment through the Insert Link >> Web Link
3. A user can add an attachment link through Insert Link >> Search and search for the attachment.  

Steps to Reproduce

1. Add an attachment to a page using scenario 1, 2 and 3 above. 
2. Log in as a user who do not have permissions to view the said attachment and visit the page.
3. For scenario 1 and 2, when the user clicks on the link Confluence redirects the user to a Page not found error.
4. For scenario 3, the link will be grayed out and when you click on the link Confluence just refreshes the same page.

Expected Results

The behaviour should be standard with all the above scenarios. Preferably that the user gets redirected to the page not found error page. 

Actual Results

Different behaviours depending on the different approach users are adding attachment links.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available