Concepts,,,,(සංකල්ප)

https://newbedev.com/only-authenticate-with-google-auth-provider-if-user-exists

Firebase nodejs operations are async and the request like check the exhistance and then proceed with reminder need to be done is sync way using promises . This requires to done using firebase admin client if you are developing rest api and  follwing function is a example for it. usersRef.orderByChild('email').equalTo(result.email).once('value').then(function(snapshot) {                     isExhist= snapshot.exists();                       if (isExhist) {                        }                   else {                    } });