@Override
  public PrincipalKeyCredential getKDCAdministratorCredentials(String clusterName) throws AmbariException {
    Credential credentials = credentialStoreService.getCredential(clusterName, KDC_ADMINISTRATOR_CREDENTIAL_ALIAS);

    if (credentials instanceof PrincipalKeyCredential) {
      return (PrincipalKeyCredential) credentials;
    } else {
      return null;
    }
  }
Gets the previously stored KDC administrator credential.
<p/>
This implementation accesses the secure CredentialStoreService instance to get the data.

@param clusterName the name of the relevant cluster
@return a PrincipalKeyCredential or null, if the KDC administrator credential is not available
@throws AmbariException if an error occurs while retrieving the credentials
ambari-server/src/main/java/org/apache/ambari/server/controller/KerberosHelperImpl.java