I have a folder called '[Home]' that mounts an SMB in another server, using session credential, enable for all users and using "$user" in mapping option, so the folder is mounted as "/server/sharing/". This is working fine, but I can't share anything inside this sharing/folder....note that "Enable sharing" is enabled for this external storage, but still not able to share. In the user end, when I go to details=>share, just got "Resharing is not allowed". Is this a bug? My guess is that is not possible to share a mounted-folder using session credentials....simples because after session use, credentials are not available anymore (like when public is trying to access sharing URL). If is this the problem, "Enable sharing" shouldn't be available in storage configuration.
Also, in "External Storage" panel, when I select "Allow sharing on user-mounted external storages" in the bottom of page (not in specific mounting point/folder!), I got an "Saved" after select/de-select.....but if I reload page, the checkbox is de-selected again.
Log-in credentials, save in session Credentials are only stored in the session and not captured in the database. Files cannot be shared, as credentials are not stored.
What you need:
Log-in credentials, save in database Credentials are stored in the database, and files can be shared.
The drawbacks are that sharing is disabled when this mechanism is in use, as ownCloud has no access to the storage credentials, and background file scanning does not work.