docs: public ApiResponse authorizeAppClient(String clientId, String clientSecret) {
          validateNonEmptyParam(clientId, "client identifier");
          validateNonEmptyParam(clientSecret, "client secret");
          assertValidApplicationId();
          loggedInUser = null;
          accessToken = null;
          currentOrganization = null;
          Map<String, Object> formData = new HashMap<String, Object>();
          formData.put("grant_type", "client_credentials");
          formData.put("client_id", clientId);
          formData.put("client_secret", clientSecret);
          ApiResponse response = apiRequest(HttpMethod.POST, formData, null,
                  organizationId, applicationId, "token");
          if (response == null) {
              return response;
          }
          if (!isEmpty(response.getAccessToken())) {
              loggedInUser = null;
              accessToken = response.getAccessToken();
              currentOrganization = null;
              log.info("Client.authorizeAppClient(): Access token: "
                      + accessToken);
          } else {
              log.info("Client.authorizeAppClient(): Response: " + response);
          }
          return response;
      }