@Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
      safeWrite(ctx, ctx.alloc().buffer(4).writeInt(SASL_TRANSFER_MAGIC_NUMBER));
      byte[] firstMessage = new byte[0];
      if (saslClient.hasInitialResponse()) {
        firstMessage = saslClient.evaluateChallenge(firstMessage);
      }
      sendSaslMessage(ctx, firstMessage);
      ctx.flush();
      step++;
    }
Create a ByteString from byte array without copying (wrap), and then set it as the payload
for the builder.
@param builder builder for HDFS DataTransferEncryptorMessage.
@param payload byte array of payload.
hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/FanOutOneBlockAsyncDFSOutputSaslHelper.java