docs: @Reference(cardinality = ReferenceCardinality.MULTIPLE,
                 policyOption = ReferencePolicyOption.GREEDY)
      protected synchronized void setCustomUserRegistry(com.ibm.websphere.security.UserRegistry externalUserRegistry, Map<String, Object> props) {
          String id = getId(props);
          customUserRegistries.put(id, externalUserRegistry);
      }