как получить код авторизации для OAuth

Question

Я застрял на получении кода авторизации.Кто-нибудь, помогите мне сделать это возможным.

public String getAuthCode(String authUrl, String userName, String password, String scope, String clientId, 
    String redirectUrl) throws ClientProtocolException, IOException, URISyntaxException{
DefaultHttpClient httpclient = new DefaultHttpClient();

System.out.println("Adding Paramters to a Array List as NameValuePair");
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("scope", scope));
params.add(new BasicNameValuePair("response_type", "code"));
params.add(new BasicNameValuePair("client_id", clientId));
params.add(new BasicNameValuePair("redirect_uri", redirectUrl));

System.out.println("Parameters List:" + params);

System.out.println("Building the URI with Authorization Endpoint by adding the Parameters create in Array List");
URI uri = new URIBuilder(authUrl)
        .addParameters(params)
        .build();
System.out.println("Built URI:" + uri);

System.out.println("Creating HTTPGET with the Created URI");
HttpGet get = new HttpGet(uri);
System.out.println("HttpGet:" + get);

System.out.println("Creating Client Context");
HttpClientContext context = HttpClientContext.create();
System.out.println("Created Client Context:" + context);


System.out.println("Executing the GET Method with the created Client Context");
HttpResponse response = httpclient.execute(get, context);
System.out.println("HttpResponse:" + response);

System.out.println("Getting the Final URI from the Submitted Get Method");
URI finalUrl = get.getURI();
System.out.println("Final URL:" + finalUrl);

System.out.println("Creating a List of URI from the Redirection Locations using Client Context");
List<URI> locations = context.getRedirectLocations();
System.out.println("List of URI:" + locations);

if (locations != null) {
    finalUrl = locations.get(locations.size() - 1);
}
System.out.println("Taking the last URL as Final:" + finalUrl);

System.out.println("Creating Entity");
EntityUtils.consume(response.getEntity());
System.out.println("Consume the Entity:" + response.getEntity());

String userid = "username=".concat(userName);
System.out.println("UserID:" + userid);
String userPassword = "Password=".concat(password);
System.out.println("User Password:" + userPassword);
String cred = userid+"&"+userPassword;
System.out.println("User Credentials:" + cred);
HttpPost postReq = new HttpPost(finalUrl);
StringEntity entity = new StringEntity(cred);
postReq.setEntity(entity);
postReq.addHeader("Content-Type", "application/x-www-form-urlencoded"); 
postReq.addHeader("User-Agent", "MSIE 8.0");


HttpResponse responsePost = httpclient.execute(postReq,context);
List<Header> location = Arrays.asList(responsePost.getHeaders("Location"));
String locationUrl = location.get(0).getValue().toString();
String[] locationArray = locationUrl.split("=");
String authCode = locationArray[1].trim().toString();
//System.out.println(authCode);

EntityUtils.consume(responsePost.getEntity());
System.out.println("Response Post Entity:"+responsePost);
System.out.println("Authorization Code:" +authCode);
return authCode;}

Ошибка:

[ОШИБКА] 2018-10-11 19: 42: 29.085 [http-nio-8080-exec-1] [dispatcherServlet] - Servlet.service () для сервлета [dispatcherServlet] в контексте с путем [] вызвала исключение [Ошибка обработки запроса;вложенное исключение - java.lang.ArrayIndexOutOfBoundsException: 0] с основной причиной java.lang.ArrayIndexOutOfBoundsException: 0 в java.util.Arrays $ ArrayList.get (Arrays.java:3841) ~ [?: 1.8.0_102] в com.vonCon.FreshDesk.Vbs.TokenContorller.getAuthCode (TokenContorller.java:119) ~ [classes / :?]