已注册的用户只应进行一次身份验证

伙计们，我正在安卓2.2上工作。我有一种情况，当用户进入应用程序时，他将被允许使用提供的默认音频文件。

现在有一个按钮，当他点击它就会进入登录页面。如果他不是注册用户，他可以注册自己，然后使用用户名和密码再次登录。一旦他使用用户名和密码登录，他将被允许从服务器下载n个音频文件。

因此，我想做的是，一旦用户是注册用户并登录并退出应用程序，但如果注册用户想下载更多文件，则不应提示他用户名和密码，因为他是注册用户。

如何做到这一点？

注册用户登录代码：

ArrayList<NameValuePair> nvp = new  ArrayList<NameValuePair>();
             nvp.add(new BasicNameValuePair("userid", userid.getText().toString()));
             nvp.add(new BasicNameValuePair("password", password.getText().toString()));
             String un = userid.getText().toString();
             String pass = password.getText().toString();
             System.out.println("user name is " + un);
             System.out.println("password is " +pass);
//           Log.e(""+sid.getText().toString(),"0"); 
//           Log.e(""+sname.getText().toString(),"0");
                try {
                HttpClient httpclient = new DefaultHttpClient();
                HttpPost httppost = new HttpPost("http://mywebsite.com/login.php");
                httppost.setEntity(new UrlEncodedFormEntity(nvp));
                HttpResponse response = httpclient.execute(httppost);
                HttpEntity entity = response.getEntity();
                is = entity.getContent();
                } catch(Exception e){
                    Log.e("log_tag", "Error in http connection"+e.toString());
                }
                try {
                    BufferedReader bf  = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
                    sb = new StringBuilder();
                    sb.append(bf.readLine()+ "'n");
                    String line="0";
                       while ((line = bf.readLine()) != null) {
                                      sb.append(line + "'n");
                        }
                        is.close();
                        result=sb.toString();
                    System.out.println("value of result " +result);
                    if(result.contains(auth)){
                        System.out.println("username and password is correct");
                        Intent authorised = new Intent(Login.this,BrowseFiles.class);
                        startActivity(authorised);
                    }else{
                        System.out.println("incorrect wrong wrong wrong");
                        error.setText("Incorrect username and password");
                    }

                }catch(Exception e){
                      Log.e("log_tag", "Error converting result "+e.toString());
                }