@Override
      public byte[] run() throws Exception {
        return saslRpcClient.evaluateChallenge(challenge);
      }
@param saslPromise {@code true} if success, {@code false} if server tells us to fallback to
                   simple.
hbase-client/src/main/java/org/apache/hadoop/hbase/security/NettyHBaseSaslRpcClientHandler.java