<script>
  // Get elements
  const txtEmail = document.getElementById('txtEmail');
  const txtPassword = document.getElementById('txtPassword');
  const btnDoLogin = document.getElementById('btnDoLogin');

  // Login event
  btnDoLogin.addEventListener('click', e => {
    // Get email and password
    const email = txtEmail.value;
    const password = txtPassword.value;
    const auth = firebase.auth();
    // Sign in
    const promise = auth.signInWithEmailAndPassword(email, password);
    promise.catch(e => document.getElementById("errorThings").innerHTML = e.message);
  });

  // Add realtime listener
  firebase.auth().onAuthStateChanged(firebaseUser => {
    if(firebaseUser){
      firebase.auth().currentUser.getIdToken(/* forceRefresh */ true).then(function(idToken) {
        console.log(idToken)
        window.location = '/doLoginIn/' + idToken;
        // Send token to your backend via HTTPS
        // ...
      }).catch(function(error) {
        // Handle error
      });

    } else {
      console.log('not logged in');
    }
  });
</script>

decoded_token = auth.verify_id_token(id_token)

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

@app.route("/doLoginIn")
@app.route("/doLoginIn/<id_token>")
def doLoginIn(id_token=None):
    try:
        decoded_token = auth.verify_id_token(id_token)
        print(decoded_token)
        session['email'] = decoded_token['email']
        session['loggedOn'] = True
        return redirect("/dashboard")
    except:
        return redirect("/login")

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