HttpsURLConnection conn =
          Util.getUrlConnection("https://test.salesforce.com/services/oauth2/token");
conn.setDoOutput(true);
conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

conn.setRequestProperty("charset", "utf-8");
conn.setUseCaches(false);

String urlParameters = String.format("grant_type=password&client_id=%s&client_secret=%s&username=%s&password=%s",
(Object[])new String[] {SalesforceCommunicator.APP_CONSUMER_KEY, SalesforceCommunicator.APP_CONSUMER_SECRET, credentials.first, credentials.second});

byte[] postData = urlParameters.getBytes(StandardCharsets.UTF_8);
conn.setRequestProperty("Content-Length", Integer.toString(postData.length));

DataOutputStream wr = new DataOutputStream(conn.getOutputStream());
wr.write(postData);

String response = Util.readResponse(conn.getInputStream());
JSONObject jsonResponse = new JSONObject(response);