I am struggling to understand Firebase authentication on the client/server side and have the question below.

I have a login.html page with a login-form and submit button. On the button click event, I have a JavaScript to do some client validation and perform the authentication):

btnSignIn.addEventListener('click', e => {
    // Get email/pass
    const email = inputEmail.value;
    const pass = inputPassword.value;
    /* to-do some validation and then sign in */
    // Sign in
    const promise = firebase.auth().signInWithEmailAndPassword(email, pass)
    promise.catch(e => console.log(e.message))
    }            
});

This is working great so far. Now, once the user has logged in, I want to redirect to home.html page but since this page should be protected by authorized users, do I need to send the token to the server (which is a Flask app)?

How do I send the token from JS to my Flask app? I saw in the Firebase docs that the way to go is via ajax. From the documentation, this is how I should send the token but I am not sure how to implement it.

firebase.auth().currentUser.getIdToken(/* forceRefresh */ true).then(function(idToken) {
  // Send token to your backend via HTTPS
  // ...
}).catch(function(error) {
  // Handle error
});

My test Flask app:

@app.route('/')
@app.route('/home')
def home():
    return render_template("home.html")

@app.route('/login', methods=['GET', 'POST'])
def login():
    return render_template("login.html")