code: public static JSONObject oauth(String apiKey, String secretKey, AipClientConfiguration config) {
          try {
              AipRequest request = new AipRequest();
              request.setUri(new URI(AipClientConst.OAUTH_URL));
              request.addBody("grant_type", "client_credentials");
              request.addBody("client_id", apiKey);
              request.addBody("client_secret", secretKey);
              request.setConfig(config);
              int statusCode = 500;
              AipResponse response = null;
              // add retry
              int cnt = 0;
              while (statusCode == 500 && cnt < 3) {
                  response = AipHttpClient.post(request);
                  statusCode = response.getStatus();
                  cnt++;
              }
              String res = response.getBodyStr();
              if (res != null && !res.equals("")) {
                  return new JSONObject(res);
              } else {
                  return Util.getGeneralError(statusCode, "Server response code: " + statusCode);
              }
          } catch (URISyntaxException e) {
              e.printStackTrace();
          }
          return Util.getGeneralError(-1, "unknown error");
      }
docs: get access_token from openapi
  @param apiKey API key from console
  @param secretKey Secret Key from console
  @param config network config settings
  @return JsonObject of response from OAuth server