code: byte[] readSignResponse() throws IOException {
      // Read the first 9 bytes from the InputStream which are the SSH2_AGENT_SIGN_RESPONSE headers.
      final byte[] headerBytes = readBytes(9, "SSH2_AGENT_SIGN_RESPONSE");
      log.debug("Received SSH2_AGENT_SIGN_RESPONSE message from ssh-agent.");
      final SignResponseHeaders headers = SignResponseHeaders.from(headerBytes);
  
      // Read the rest of the SSH2_AGENT_SIGN_RESPONSE message from ssh-agent.
      // 5 is the sum of the number of bytes of response code and response length
      final byte[] bytes = readBytes(headers.getLength() - 5);
      final ByteIterator iterator = new ByteIterator(bytes);
      final byte[] responseType = iterator.next();
  
      final String signatureFormatId = new String(responseType);
      if (!signatureFormatId.equals(Rsa.RSA_LABEL)) {
        throw new RuntimeException("I unexpectedly got a non-Rsa signature format ID in the "
                                   + "SSH2_AGENT_SIGN_RESPONSE's signature blob.");
      }
  
      return iterator.next();
    }
docs: Return an array of bytes from the ssh-agent representing data signed by a private SSH key.
  @return An array of signed bytes.