allow snap apps to access data from outside of container

Question

I installed libreoffice from snap. The program works fine but I'm locked in the snap container. Trying to open an office attachment in Evolution results in:

Access to /home/user/.cache/evolution/tmp/evolution-user/Document.xlsx was denied.

I get the idea that snap packages are self contained and secure, but in order to work within a system other packages that were installed from .deb should be granted access to snap. How can I do this without compromising security?

Update: In response to user spktkpkt, when I list

$snap interfaces

Slot                     Plug
:bluetooth-control       -
...
:gsettings               emacs-tealeg
:hardware-observe        canonical-livepatch
:home                    emacs-tealeg,libreoffice

I can see that libreoffice is connected to :home but, maybe because my document is in a hidden folder (.cache) it can't be accessed.

Note that home interface can only access non-hidden files as described on the interfaces reference page of snap:

[home Interface] Can access non-hidden files in user's $HOME and gvfs mounted directories owned by the user to read/write/lock.

Answer 1

I have not used it yet, but there should be a interface to communicate with the $HOME directory. Here is some information about interfaces and here is a list with all available interfaces.