...
"projections" : [
  "default:/federation => /",
]
...

Node root1 = session.getNode("/");
NodeIterator it = root1.getNodes();
while (it.hasNext()){
   Node node = (Node)it.next();
   System.out.println(node.getName()+" => "+node.getIdentifier());
}

federation => 94dd693eaa9871/
jcr:system => 9db8771317f1e7jcr:system
federation => 4feed675-bbfe-49a5-af07-83952b778bb2