Google Authentication get access token using refresh token - push-notification

Question

I am using Push Notifications API for integrating client's calendar event. I have created channel also. But I am not able to get refresh token while authentication. I need to get user consent from UI and based on the verification code I am getting access token and refresh token. But when I am trying to get access token using existing refresh token, it is asking for client Id and secret. As I am just using consent from user I do not have client Id and client secret for each user. How can I resolve this for my application?
I am using below code for authentication
private static Credential getCredentials(final NetHttpTransport HTTP_TRANSPORT)
throws IOException {
// Load client secrets.
InputStream in = CalendarQuickstart.class.getResourceAsStream(CREDENTIALS_FILE_PATH);
if (in == null) {
throw new FileNotFoundException("Resource not found: " + CREDENTIALS_FILE_PATH);
}
GoogleClientSecrets clientSecrets =
GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(in));
// Build flow and trigger user authorization request.
GoogleAuthorizationCodeFlow flow =
new GoogleAuthorizationCodeFlow.Builder(HTTP_TRANSPORT, JSON_FACTORY, clientSecrets, SCOPES)
.setDataStoreFactory(new FileDataStoreFactory(new java.io.File(TOKENS_DIRECTORY_PATH)))
.setAccessType("offline")
.build();
LocalServerReceiver receiver = new LocalServerReceiver.Builder().setPort(8888).build();
return new AuthorizationCodeInstalledApp(flow, receiver).authorize("user");
}
Here is how I am calling calender API
public static void main(String... args) throws IOException, GeneralSecurityException {
// Build a new authorized API client service.
final NetHttpTransport HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
Credential credential = getCredentials(HTTP_TRANSPORT);
String accessToken = credential.getAccessToken();
Calendar service =
new Calendar.Builder(HTTP_TRANSPORT, JSON_FACTORY, googleCredential)
.setApplicationName(APPLICATION_NAME)
.build();
System.out.println(accessToken);
// List the next 10 events from the primary calendar.
DateTime now = new DateTime(System.currentTimeMillis());
Events events =
service
.events()
.list("primary")
.setMaxResults(10)
.setTimeMin(now)
.setOrderBy("startTime")
.setSingleEvents(true)
.execute();
List<Event> items = events.getItems();
if (items.isEmpty()) {
System.out.println("No upcoming events found.");
} else {
System.out.println("Upcoming events");
for (Event event : items) {
DateTime start = event.getStart().getDateTime();
if (start == null) {
start = event.getStart().getDate();
}
// System.out.printf("%s %s (%s)\n", event.getId(), event.getSummary(), event.toString());
}
}
}
}