Server-side connecting and querying Firebase from Node.JS

const firebase = require('firebase');

const firebaseConfig = {
    apiKey: '<your-api-key>',
    authDomain: '<your-domain>.firebaseapp.com',
    databaseURL: 'https://<your-domain>.firebaseio.com',
    storageBucket: '<your-domain>.appspot.com'
};

firebase.initializeApp(firebaseConfig);

const db = firebase.database();

console.log('Authenticating...');
firebase.auth().signInWithEmailAndPassword('your@email.com', 'YoUrPaSsWoRd').catch(error => {
    console.log('Error while authenticating:', error);
}).then(loginObject => {
    if (loginObject) {
        console.log('Success!!');
        // now do your thing!
        let something = db.ref('users/' + loginObject.uid + '/something');
        // do something with something
    } else {
        console.log('Oops, something went wrong while authenticating:', loginObject);
    }
});