private RpcClient createClient() throws Exception {
    return clientUGI.doAs((PrivilegedExceptionAction<RpcClient>) () -> RpcClientFactory
      .createClient(clientConf, HConstants.DEFAULT_CLUSTER_ID.toString()));
  }
Test secure client connecting to a non secure server, where we have multiple server principal
candidates for a rpc service. See HBASE-28321.
hbase-server/src/test/java/org/apache/hadoop/hbase/security/TestMultipleServerPrincipalsFallbackToSimple.java