[encryption] store keys by fileId instead of path

[mejo-]

Tip

Help move this idea forward

• Use the 👍 reaction to show support for this feature.
• Avoid commenting unless you have relevant information to add; unnecessary comments create noise for subscribers.
• Subscribe to receive notifications about status changes and new comments.

---

Is your feature request related to a problem? Please describe.
In Collectives, we can have different paths to a file by user (when a user changes their user_folder user setting). This leads to inaccessible files with server-side encryption as the encryption keys are stored by file path.

Describe the solution you'd like
In order to fix this, we should switch to fileId based key storage instead of file path based key storage.

Describe alternatives you've considered

• We could use the storage path instead for ISystemMountPoint paths, but this would come with its own problems. E.g. appdata is excluded from encryption and Collectives files live in appdata directory.
• We could introduce a way to map different user mountpoint paths to the same encryption key path.

[mejo-]

#59343 is a minimal proof of concept that fixes the concrete bug (nextcloud/collectives#2326) in Collectives.