This will neew a follow-up issue.
This patch is just preventing downloading the HTML popup code when a file is not found.
Ideally, we should be able to serve the original file using the system OAuth.
When we need to show a login link, we don't want the normal page layout because we are in an iframe
already. Use the embedded layout to reduce the clutter of the page.
Based on repository_owncloud from
https://github.com/learnweb/moodle-repository_owncloud at 5b5fdbb.
Differences to the original:
* Renamed to repository_nextcloud
* Updated version.php for core
* Removed compatibility polyfills (webdav, privacy)
* Removed boilerplate files (e.g. README, CI config)
* Implement null_provider for privacy API as personal data is neither
stored nor transmitted to the external system
