The AWS Java S3 SDK is used to generate the pre-signed DAUs with the configured duration (see the configuration settings for the repository and Content Store expiry times). The pre-signed request generates a download for the remote content.
Known limitations:
DAU generation on AWS S3 depends on the security credentials used - see Sharing an object with a presigned URL for more details.
See the GitHub project documentation for a detailed view of the main flows and other parts of the implementation.