Google Drive API - OAuth2.0: How to Automate Authentication Process? Doubts and Questions

Question

I'm trying to integrate Google APIs inside a project (Thesis project) and I have some doubts and questions. So, here it is the scenario:

I wrote a back-end application in Java that runs solely from a command-line and has absolutely no interaction with a user. Its goal is to allow communication and interaction between sensors and actuators. Everything works great. Now I'd like to integrate something in order to let the sensors backup data both with a certain periodicity and due to some detected threshold value. So I thought, why not trying with Google Drive. The first very useful links have been:

https://developers.google.com/drive/web/quickstart/quickstart-java

https://developers.google.com/accounts/docs/OAuth2InstalledApp

Quick start examples work like a charm. However it requires quite a bit of settings: create a project inside the Developer Console (therefore an account), enable Drive API, then create a Client ID and a Client Secret. Once you've done these steps, you can hard-coded client ID and secret to form the request URL for google drive. Then you're kindly asked to enter the url in a browser, log in if you're not, accept and finally copy and paste into your console the authorization code for obtaining an access token. Wow, quite a security proccess. But hey, I completely agree with it, above all in a scenario where we have either a web app, a smartphone app or a web service that needs users' authentication and authorization in order to let the app doing its job by accessing someone else account. But in my case, I just would like that sensors will backup data on my google drive.

These facts lead to my first question: in order to use Google APIs (Drive in this case), do I have to create a project anyway? Or is there another approach? If I'm not wrong, there aren't other ways to create a client Id and secret without creating a project inside the Developer Console. This puzzles me a lot. Why should I create a project to use basically some libraries?

So, let's assume the previous as justifiable constraints and move on the real question: how to automate the authentication process? Given my scenario where a sensor (simply a Java module) want to backup data, it would be impossible to complete all that steps. The google page about OAuth 2.0 has a great explanations about different scenarios where we can embed the authentication procedure, included one for "devices with limited input capabilities". Unluckily, this is more complicated then the others and requires that "The user switches to a device or computer with richer input capabilities, launches a browser, navigates to the URL specified on the limited-input device, logs in, and enters the code." (LOL)

So, I didn't give up and I ended up on this post that talks about OAuth Playground: How do I authorise an app (web or installed) without user intervention? (canonical ?). It really looks like as a solution for me, in particular when it says:

NB2. This technique works well if you want a web app which access your own (and only your own) Drive account, without bothering to write the authorization code which would only ever be run once. Just skip step 1, and replace "my.drive.app" with your own email address in step 5.

However if I'm not wrong, I think that OAuth Playground it's just for helping test and debug projects that use Google APIs, isn't it? Moreover, Google drive classes such as GoogleAuthorizationCodeFlow and GoogleCredential (used inside the Java quick start example) always need Client ID, Client Secret and so on, which brings me to point zero (create a project and do the whole graphical procedure).

In conclusion: is there a way to avoid the "graphical" authentication interaction and convert it into an automated process using only Drive's APIs without the user intervention? Thanks a lot, I would be grateful for any tip, hint, answer, pointer :-)

Answer 1

This is just a snippet of code that I wrote thanks to pinoyyid suggestions. Just to recap what we should do in this case (when in your program there isn't a user interaction for completing all the Google GUI authentication process). As reported in https://developers.google.com/drive/web/quickstart/quickstart-java

1. Go to the Google Developers Console.
2. Select a project, or create a new one.
3. In the sidebar on the left, expand APIs & auth. Next, click APIs. In the list of APIs, make sure the status is ON for the Drive API.
4. In the sidebar on the left, select Credentials.

In either case, you end up on the Credentials page and can create your project's credentials from here.

From the Credentials page, click Create new Client ID under the OAuth heading to create your OAuth 2.0 credentials. Your application's client ID, email address, client secret, redirect URIs, and JavaScript origins are in the Client ID for web application section.

The pinoyyd post is neater and get straight to the point: How do I authorise a background web app without user intervention? (canonical ?) Pay attention to step number 7

Finally the snippet of code is very simple, it's just about sending a POST request and it's possible to do that in many ways in Java. Therefore this is just an example and I'm sure there is room for improvements ;-)

// Both to set access token the first time that we run the module and in general to refresh the token
public void sendPOST(){
  try {
      URL url = new URL("https://www.googleapis.com/oauth2/v3/token");
      Map<String,Object> params = new LinkedHashMap<>();
      params.put("client_id", CLIENT_ID);
      params.put("client_secret", CLIENT_SECRET);
      params.put("refresh_token", REFRESH_TOKEN);
      params.put("grant_type", "refresh_token");

      StringBuilder postData = new StringBuilder();
      for (Map.Entry<String,Object> param : params.entrySet()) {
          if (postData.length() != 0) postData.append('&');
          postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
          postData.append('=');
          postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
      }
      byte[] postDataBytes = postData.toString().getBytes("UTF-8");

      HttpsURLConnection conn = (HttpsURLConnection)url.openConnection();
      conn.setRequestMethod("POST");
      conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
      conn.setRequestProperty("Content-Length", String.valueOf(postDataBytes.length));
      conn.setDoOutput(true);
      conn.getOutputStream().write(postDataBytes);

      BufferedReader in_rd = new BufferedReader(new InputStreamReader(conn.getInputStream(), "UTF-8"));

      // Read response body which should be a json structure
      String inputLine;
      StringBuilder responseBody = new StringBuilder();

      while ((inputLine = in_rd.readLine()) != null) {
              responseBody.append(inputLine);
      }
      in_rd.close();

      //Parsing Response --> create a json object
      JSONObject jsonResp = new JSONObject(responseBody);

      //Modify previous access token String
      ACCESS_TOKEN = jsonResp.getString("access_token");

  }

  catch(MalformedURLException ex_URL){
      System.out.println("An error occured: " + ex_URL.getMessage());
  }
  catch(JSONException ex_json) {
      System.out.println("An error occured: " + ex_json.getMessage());             
  }
  catch(IOException ex_IO){
      System.out.println("An error occured: " + ex_IO.getMessage());
  }

} //end of sendRefreshPOST method

Hope this snippet of code will help others that will face the same situation !