HDDS-2226. S3 Secrets should use a strong RNG. (#1572)

(cherry picked from commit d59bcbfa0f30fc6fedb0a7e1896292a524ff71c7)
diff --git a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java
index 25bfc29..5b47876 100644
--- a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java
+++ b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java
@@ -30,6 +30,7 @@
 import java.nio.file.Paths;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Optional;
@@ -39,7 +40,6 @@
 import org.apache.commons.compress.archivers.tar.TarArchiveEntry;
 import org.apache.commons.compress.archivers.tar.TarArchiveOutputStream;
 import org.apache.commons.compress.utils.IOUtils;
-import org.apache.commons.lang3.RandomStringUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdds.scm.HddsServerUtil;
@@ -70,6 +70,8 @@
  */
 public final class OmUtils {
   public static final Logger LOG = LoggerFactory.getLogger(OmUtils.class);
+  private static final SecureRandom SRAND = new SecureRandom();
+  private static byte[] randomBytes = new byte[32];
 
   private OmUtils() {
   }
@@ -246,9 +248,9 @@
 
   public static byte[] getSHADigest() throws IOException {
     try {
+      SRAND.nextBytes(randomBytes);
       MessageDigest sha = MessageDigest.getInstance(OzoneConsts.FILE_HASH);
-      return sha.digest(RandomStringUtils.random(32)
-          .getBytes(StandardCharsets.UTF_8));
+      return sha.digest(randomBytes);
     } catch (NoSuchAlgorithmException ex) {
       throw new IOException("Error creating an instance of SHA-256 digest.\n" +
           "This could possibly indicate a faulty JRE");