Firebase authentication (is not a function, is not a constructor) - node.js

Question

I don't know what is wrong. I'm using Node.js and trying to log in using email/password and Google authentication. I have enabled all of them in Firebase console.
npm Firebase version - 3.1.0
part of code:
var firebase = require('firebase');
var config = {
apiKey: "AIzaSyAH27JhfgCQfGmoGTdv_VaGIaX4P-qAs_A",
authDomain: "pgs-intern.firebaseapp.com",
databaseURL: "https://pgs-intern.firebaseio.com",
storageBucket: "pgs-intern.appspot.com",
};
firebase.initializeApp(config);
app.post('/login', function(req, res) {
var auth = firebase.auth();
firebase.auth().signInWithEmailAndPassword(req.body.login, req.body.password).catch(function(error) {
// Handle Errors here.
var errorCode = error.code;
var errorMessage = error.message;
// ...
});
}
Error: firebase.auth(...).signInWithLoginAndPassword is not a function
or
Error: firebase.auth(...).GoogleAuthProviders is not a constructor when I write
firebase.auth().signInWithPopup(provider).then(function(result) {
// This gives you a Google Access Token. You can use it to access the Google API.
var token = result.credential.accessToken;
// The signed-in user info.
var user = result.user;
// ...
}).catch(function(error) {
// Handle Errors here.
var errorCode = error.code;
var errorMessage = error.message;
// The email of the user's account used.
var email = error.email;
// The firebase.auth.AuthCredential type that was used.
var credential = error.credential;
// ...
});
I just did exactly what is in documentation.

Answer 1

Your first error probably comes from a typo somewhere.
firebase.auth(...).signInWithLoginAndPassword is not a function
Notice it says signInWithLoginAndPassword, the function is called signInWithEmailAndPassword. In the posted code it's used correctly, so it's probably somewhere else.
firebase.auth(...).GoogleAuthProviders is not a constructor
You have not posted the code where you use this, but I assume this error happens when you create your provider variable, that you use in firebase.auth().signInWithPopup(provider)
That line should be var provider = new firebase.auth.GoogleAuthProvider();
Based on the error message, I think you might be doing new firebase.auth().GoogleAuthProvider(); Omit the brackets after auth, if that's the case.

Answer 2

Do not call GoogleAuthProvider via an Auth() function.
According to the documentation you have to create an instance of GoogleAuthProvider.
let provider = new firebase.auth.GoogleAuthProvider()
Please check the following link https://firebase.google.com/docs/auth/web/google-signin

Answer 3

There is no way to sign your node.js app into firebase with email+password or one of the social providers.
Server-side processes instead sign into Firebase using so-called service accounts. The crucial difference is in the way you initialize the app:
var admin = require('firebase-admin');
admin.initializeApp({
serviceAccount: "path/to/serviceAccountCredentials.json",
databaseURL: "https://databaseName.firebaseio.com"
});
See this page of the Firebase documentation for details on setting up a server-side process.