URL url = new URL("https://student.psu.ru/pls/stu_cus_et/stu.login");
HttpsURLConnection connection = (HttpsURLConnection)url.openConnection();

String params = "p_redirect=stu.teach_plan&p_username="+URLEncoder.encode(login, "windows-1251")+"&p_password="+password;
connection.setRequestMethod("POST");
connection.setDoOutput(true);
DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
wr.writeBytes(params);
wr.flush();
wr.close();