How do you restrict Google Login (Oauth2) to emails from a specific Google Apps domain for a Flask WebApp?

Question

Developing a Flask app (Python3/Heroku) for internal company use and successfully implemented Google Login (Oauth2) based on brijieshb42\'s article which uses requests_oauthlib.

Answer 1

When you create the authorization URL, you can append optional parameters; appending hd= ... will do the trick:

auth_url, state = google.authorization_url(AUTH_URI, access_type='offline', hd='savv.ch')

This has many benefits. For example Google will then automatically pick the right account (if it matches the domain), which potentially saves a step in the Auth process, if the user is logged into multiple accounts.

http://requests-oauthlib.readthedocs.io/en/latest/api.html#requests_oauthlib.OAuth2Session.authorization_url

Answer 2

After successful authentication, you have to check the provided email yourself. I have added the code snippet from the my article that you have referenced. I have added the extra check required in after comment.

@app.route('/gCallback')
def callback():
    # Redirect user to home page if already logged in.
    if current_user is not None and current_user.is_authenticated():
        return redirect(url_for('index'))
    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 = get_google_auth(state=session['oauth_state'])
        try:
            token = google.fetch_token(
                Auth.TOKEN_URI,
                client_secret=Auth.CLIENT_SECRET,
                authorization_response=request.url)
        except HTTPError:
            return 'HTTPError occurred.'
        google = get_google_auth(token=token)
        resp = google.get(Auth.USER_INFO)
        if resp.status_code == 200:
            user_data = resp.json()
            email = user_data['email']
            """
            Your Domain specific check will come here.
            """
            if email.split('@')[1] != 'domain.com':
                flash('You cannot login using this email', 'error')
                return redirect(url_for('login'))
            user = User.query.filter_by(email=email).first()
            if user is None:
                user = User()
                user.email = email
            user.name = user_data['name']
            print(token)
            user.tokens = json.dumps(token)
            user.avatar = user_data['picture']
            db.session.add(user)
            db.session.commit()
            login_user(user)
            return redirect(url_for('index'))
        return 'Could not fetch your information.'