how to check if phone exists in firebase auth

Question

hey I try to check if the phone number that user is insert is exist in my firebase auth (LoginActivity) I try in this way

String phoneNumber = "+1234567890";

mAuth.fetchSignInMethodsForEmail(phoneNumber)
        .addOnCompleteListener(new OnCompleteListener<SignInMethodQueryResult>() {
            @Override
            public void onComplete(@NonNull Task<SignInMethodQueryResult> task) {
                if (task.isSuccessful()) {
                    SignInMethodQueryResult result = task.getResult();
                    List<String> signInMethods = result.getSignInMethods();
                    if (signInMethods.contains("phone")) {
                        // Phone number is already in use in Firebase Auth
                    } else {
                        // Phone number is not in use in Firebase Auth
                    }
                } else {
                    // An error occurred
                }
            }
        });

and when it comes to this function the debugger jump for it and don't doing anything.addOnCompleteListener(new OnCompleteListener() {

I try with firebase sdk admin and it also doesn't works can anyone know how to solve this?

Answer 1

There are three ways in which you can solve this problem. Two options are on the client, using Java code, and another one using Admin SDK.

Solution 1

When a user signs in for the first time into your app, then save user data in Firestore using a schema that looks like this:

db
|
--- users (collection)
     |
     --- $uid (document)
          |
          --- phoneNumber: "+1234567890"

To check if a user with the +1234567890 already exists, then you have to perform a query that looks like this in Java:

FirebaseFirestore db = FirebaseFirestore.getInstance();
Query queryPhoneNumber = db.collection("users").whereEqualTo("phoneNumber", "+1234567890");
queryPhoneNumber.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (QueryDocumentSnapshot document : task.getResult()) {
                if (document.exists()) {
                    Log.d(TAG, "User already exists.");
                } else {
                    Log.d(TAG, "User doesn't exist.");
                }
            }
        } else {
            Log.d(TAG, task.getException().getMessage()); //Never ignore potential errors!
        }
    }
});

Solution 2

Another more elegant and easy solution would be to use Query#count() method:

queryPhoneNumber.count();

If the result is > 0 then it means that the user already exists, otherwise it doesn't exist.

Solution 3

The last solution would be to use a Callable Cloud Function that can be called from your app . Because we use the Admin SDK in Cloud Functions you can call the getUserByPhoneNumber() method. In code it will look like this:

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.checkPhoneNumberExists = functions.https.onCall((data, context) => {
    return admin.auth()
        .getUserByPhoneNumber(data.phoneNumber)
        .then((userRecord) => {
            return { phoneNumber: true }
        })
        .catch((error) => {
            throw new functions.https.HttpsError('invalid-argument', "phoneNumber doesn't exist");
        });

});

Using this approach, there is no need to save user data in Firestore. The Admin SDK will directly query the FirebaseAuth service.