Distributed resources need to be protected against unauthorized downloads
With stream security, a contract is being established between Opencast and the distribution servers to protect distributed artifacts from being downloaded by unauthorized users.
The implementation in Opencast ensures that requests to those artifacts are authorized via a policy and then signed to ensure the policy cannot be altered. On the other end, mechanisms are implemented to verify the signature and interpret the policy to decide whether the request should be served or not. Since the policy contains a maximum valid time, donwload links can only be misused for a short amount of time.
Stream security has been merged into develop a while ago and is therefore part of Opencast 2.2.