private List<KerberosIdentityDescriptor> skipUsed() throws AmbariException {
    return candidateIdentities.stream().filter(each -> !usedIdentities.contains(each)).collect(toList());
  }
Remove all identities which are related to the specified set of components and not used by
other services or components
ambari-server/src/main/java/org/apache/ambari/server/controller/utilities/RemovableIdentities.java