String url = LoginConstants.URL_OAUTH;
HttpClient client = HttpClientBuilder.create().build();
HttpPost post = new HttpPost(url);

post.addHeader(HttpHeaders.AUTHORIZATION, LoginConstants.BASIC_AUTHORIZATION);
post.addHeader("Content-Type", ContentType.APPLICATION_FORM_URLENCODED.getMimeType());

List<NameValuePair> body = new ArrayList<NameValuePair>();
body.add(new BasicNameValuePair(LoginConstants.GRANT_TYPE, LoginConstants.GRANT_TYPE_VALUE));
body.add(new BasicNameValuePair(LoginConstants.USER_NAME, user));
body.add(new BasicNameValuePair(LoginConstants.PASSWORD, password));
body.add(new BasicNameValuePair(LoginConstants.SCOPE, LoginConstants.SCOPE_VALUE));

UrlEncodedFormEntity entity = new UrlEncodedFormEntity(body, CharEncoding.UTF_8);
post.setEntity(entity);

HttpResponse response = client.execute(post);

OkHttpClient client = new OkHttpClient();

MediaType mediaType = MediaType.parse("application/x-www-form-urlencoded");
RequestBody body = RequestBody.create(mediaType, "grant_type=password&username=canido&password=canido08&scope=customScope");
Request request = new Request.Builder()
  .url("https://localhost:7001/OAuth/token")
  .post(body)
  .addHeader("authorization", "Basic XXX")
  .addHeader("content-type", "application/x-www-form-urlencoded")
  .addHeader("cache-control", "no-cache")
  .addHeader("postman-token", "b81569ff-5f3f-f009-d512-ef4258808e01")
  .build();

Response response = client.newCall(request).execute();