As Jesse pointed out, contextual information is often useful in authenticating the build, which means we need to take Queue.Item (initially AbstractBuild was the parameter, which provided the context, and I failed to accommodate that in transition to AbstractProject.)

To still allow Queue.Tasks to provide a meaningful value fallback to Queue.Task.getDefaultAuthentication() as opposed to hard code it to ACL.SYSTEM. This allow plugins like remote-terminal-access to supply a meaningful secure value without forcing a configuration change to the user.