Firebase user authentication for java application (Not Android)

Question

I want to create a user authentication form for my java application using firebase. The dependencies for connection to the realtime database is available and the use of Firebase Admin is well documented here .

But presently Firebase Admin supports user authentication only for Node.js and it is documented here .

Here is my test code.

public class Login {
    private JPanel jPanel;

    public static void main(String[] args) {
//        Show My Form
        JFrame jFrame = new JFrame("Login");
        jFrame.setContentPane(new Login().jPanel);
        jFrame.pack();
        jFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        jFrame.setVisible(true);

//        Firebase
        FirebaseOptions options = null;
        try {
            options = new FirebaseOptions.Builder()
                    .setServiceAccount(new FileInputStream("xxx.json"))
                    .setDatabaseUrl("https://xxx.firebaseio.com/")
                    .build();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

        if (options != null) {
            FirebaseApp.initializeApp(options);
            DatabaseReference ref = FirebaseDatabase.getInstance().getReference("Clip");
            ref.addValueEventListener(new ValueEventListener() {
                public void onDataChange(DataSnapshot dataSnapshot) {
                    System.out.println("ClipText = [" + dataSnapshot.getValue() + "]");
                }

                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }
    }
}

Can anyone please guide me how can I create user authentication (eg Create user using email & password, Sign in) for my java application?

Note: I'm using Gradle.

Answer 1

Basing on the REST API documentation here: https://firebase.google.com/docs/reference/rest/auth/ i created a singleton like that to get a valid token from email and password and to validate it using the getAccountInfo method:

import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;

public class FireBaseAuth {

    private static final String BASE_URL = "https://www.googleapis.com/identitytoolkit/v3/relyingparty/";
    private static final String OPERATION_AUTH = "verifyPassword";
    private static final String OPERATION_REFRESH_TOKEN = "token";
    private static final String OPERATION_ACCOUNT_INFO = "getAccountInfo";

    private String firebaseKey;

    private static FireBaseAuth instance = null;

    protected FireBaseAuth() {
       firebaseKey = "YOUR FIREBASE KEY HERE";
    }

    public static FireBaseAuth getInstance() {
      if(instance == null) {
         instance = new FireBaseAuth();
      }
      return instance;
    }

    public String auth(String username, String password) throws Exception { 

        HttpURLConnection urlRequest = null;
        String token = null;

        try {
            URL url = new URL(BASE_URL+OPERATION_AUTH+"?key="+firebaseKey);
            urlRequest = (HttpURLConnection) url.openConnection();
            urlRequest.setDoOutput(true);
            urlRequest.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
            OutputStream os = urlRequest.getOutputStream();
            OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");
            osw.write("{\"email\":\""+username+"\",\"password\":\""+password+"\",\"returnSecureToken\":true}");
            osw.flush();
            osw.close();

            urlRequest.connect();

            JsonParser jp = new JsonParser(); //from gson
            JsonElement root = jp.parse(new InputStreamReader((InputStream) urlRequest.getContent())); //Convert the input stream to a json element
            JsonObject rootobj = root.getAsJsonObject(); //May be an array, may be an object. 

            token = rootobj.get("idToken").getAsString();

        } catch (Exception e) {
            return null;
        } finally {
            urlRequest.disconnect();
        }

        return token;
    }

    public String getAccountInfo(String token) throws Exception {

        HttpURLConnection urlRequest = null;
        String email = null;

        try {
            URL url = new URL(BASE_URL+OPERATION_ACCOUNT_INFO+"?key="+firebaseKey);
            urlRequest = (HttpURLConnection) url.openConnection();
            urlRequest.setDoOutput(true);
            urlRequest.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
            OutputStream os = urlRequest.getOutputStream();
            OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");
            osw.write("{\"idToken\":\""+token+"\"}");
            osw.flush();
            osw.close();
            urlRequest.connect();

            JsonParser jp = new JsonParser(); //from gson
            JsonElement root = jp.parse(new InputStreamReader((InputStream) urlRequest.getContent())); //Convert the input stream to a json element
            JsonObject rootobj = root.getAsJsonObject(); //May be an array, may be an object. 

            email = rootobj.get("users").getAsJsonArray().get(0).getAsJsonObject().get("email").getAsString();

        } catch (Exception e) {
            return null;
        } finally {
            urlRequest.disconnect();
        }

        return email;

    }

}

This not allow you to create users dinamically but suppose to have them already created on Firebase