// GET api/diagrams/DEFG12345/ACL/UserABC123
 public Diagram.ACL Get(Guid id, string userName)
 {
     Diagram.ACL acl = new Diagram.ACL();
     return acl;
 }
 // GET api/diagrams/DEFG12345/layouts/
 public Diagram.ACL Get(Guid diagramId)
 {
     Diagram.ACL acl = new Diagram.ACL();
     return acl;
 }