If your installation uses S3 as an external storage in any version before 10.3, you have to install and enable files_external_s3. Otherwise, files stored on existing S3 external storages will not be fully accessible.
To connect your Amazon S3 buckets to ownCloud, you will need:
S3 access key
S3 secret key
In the Folder name field enter a local folder name for your S3 mountpoint. If this does not exist it will be created.
In the Available for field enter the users or groups who have permission to access your S3 mount.
Enable SSL checkbox enables HTTPS connections; using HTTPS is
Optionally, you can override the hostname, port and region of your S3 server, which is required for non-Amazon servers such as Ceph Object Gateway.
Enable path style is usually not required (and is, in fact,
incompatible with newer Amazon datacenters), but can be used with
non-Amazon servers where the DNS infrastructure cannot be controlled.
Ordinarily, requests will be made with
http://bucket.hostname.domain/, but with path style enabled, requests are made with
See External Storage Configuration for additional mount options and information.
See auth_mechanisms for more information on authentication schemes.