I have encountered an extremely weird, annoying and looks like unique issues (nothing similar across searchable Internet).
I have created an App which uses SharePoint lists to manage data. One list stores data and pictures about some objects and the other lists stores operations performed on those objects. All pictures are stored on the same SharePoint site in a separate documents library.
I have set the correct permission on both SharePoint lists and libraries (various groups and control level) and this is working as expected (asked user to access the site or use direct links to pictures stored in the list).
There is no issue when the owner of the app uses play function from the make PowerApps UI or if they trying access it via shared link.
However all other users having permission for both app and SharePoint resources can't see pictures which are pulled from one list. They somehow have access to the 2nd list and all data is stored there just fine.
So I thought this will be SharePoint permission issue but not! When the affected user tried to access any resource which is called by app, his browser just asked him to confirm the AAD login and was able to display the picture in question.
I even checked connections in the app to confirm the app has all it needs (the connection to the desk library was not necessary before and I added it anyway).
What is extremely bizarre ?!"£$@ once the user would manually try to access any picture stored in the SharePoint they magically starting appearing in the app indicating the problem is within PowerApps (not checking/asking for a connection to SharePoint but "remembering" it if the user invokes it from somewhere else).
I know this is a complicated issue but any help on further troubleshooting would be great. It looks like when I do some changes I need to publish the app. Save it again and delete the previous version, publish the new one, ask the user to clear browser cache, cookies etc and before starting the app for the first time ask them also to click on a link which points to the random picture which is used by SharePoint list.
The above make app to work until the next app update or Microsoft PowerApps update...
Great breakdown, appreciate all this detail. It's great that you went to the community on this one but you're right, there seems to be some complexity to this issue beyond mere design.
This might be expected behavior, I know we have some limitations with authenticated links in canvas apps. We have suggested to users in the past that they store their images outside of SPO to ensure they render reliably. A customized form (which is sort of a special canvas app) actually works better here so that's a consideration. We don't expect this to work in the mobile experience at all right now, as well.
We're looking into a potential feature that does better support authenticated links but I don't believe we're there yet today. Just to be safe, you're free to set up a support incident so we can confirm if you're running into a limitation.