MismatchingStateError requests-oauthlib and flask_login

[reem-codes]

I am trying to implement login using flask-login and requests-oauthlib. I want it to be pretty much a single user login so I put some conditions to make sure the email used is mine and nobody else

here is my code:

@app.route('/login')
def login():
    if current_user.is_authenticated:
        return redirect(url_for('index'))
    google = OAuth2Session(Config.CLIENT_ID, scope=Config.SCOPE, redirect_uri=Config.REDIRECT_URI)
    authorization_url, state = google.authorization_url(Config.AUTH_URI,
                                                        access_type="offline", prompt="select_account")
    # State is used to prevent CSRF, keep this for later.
    session['oauth_state'] = state
    return redirect(authorization_url)


@app.route('/callback')
def callback():
    next_page = request.args.get('next')
    if not next_page or url_parse(next_page).netloc != '':
        next_page = url_for('index')
    # Redirect user to home page if already logged in.
    if current_user is not None and current_user.is_authenticated:
        return redirect(next_page)
    if 'error' in request.args:
        if request.args.get('error') == 'access_denied':
            return 'You denied access.'
        return 'Error encountered.'
    if 'code' not in request.args and 'state' not in request.args:
        return redirect(url_for('login'))
    else:
        # Execution reaches here when user has successfully authenticated our app.
        google = OAuth2Session(Config.CLIENT_ID, redirect_uri=Config.REDIRECT_URI,
                               state=session['oauth_state'])
        token = google.fetch_token(Config.TOKEN_URI, client_secret=Config.CLIENT_SECRET,
                                   authorization_response=request.url)
        session['oauth_token'] = token
        google = OAuth2Session(Config.CLIENT_ID, token=token)
        resp = google.get(Config.USER_INFO)
        if resp.status_code == 200:
            user_data = resp.json()
            email = user_data['email']
            if email == '[email protected]':
                user = m.User.query.filter_by(email=email).first()
                if user is None:
                    user = m.User()
                    user.email = email
                user.tokens = json.dumps(token)
                db.session.add(user)
                db.session.commit()
                login_user(user, remember=True)
                flash('logged in!')
                return redirect(url_for('admin_only'))
            return redirect(url_for('index'))
        return 'Could not fetch your information.'


@app.route('/logout')
def logout():
    logout_user()
    session.pop('oauth_token')
    return redirect(url_for('index'))

This code flashed "logged in!", but in truth I cannot access "admin_only" view which has login required decorator

When I read the logs, the error raised was MismatchingStateError. I looked around but I have no idea what causes it and how to go around it