public byte[] getInitialResponse() throws SaslException {
    if (saslClient.hasInitialResponse()) {
      return saslClient.evaluateChallenge(EMPTY_TOKEN);
    }
    return EMPTY_TOKEN;
  }
Computes the initial response a client sends to a server to begin the SASL challenge/response
handshake. If the client's SASL mechanism does not have an initial response, an empty token
will be returned without querying the evaluateChallenge method, as an authentication processing
must be started by client.
@return The client's initial response to send the server (which may be empty).
hbase-client/src/main/java/org/apache/hadoop/hbase/security/AbstractHBaseSaslRpcClient.java