app.py

import flask
import uuid
import httplib2
from oauth2client.client import flow_from_clientsecrets
from oauth2client.client import OAuth2Credentials, AccessTokenRefreshError
from apiclient.discovery import build

app = flask.Flask(__name__)
app.secret_key = str(uuid.uuid4())


@app.route('/')
def index():
    if 'credentials' not in flask.session:
        return flask.redirect(flask.url_for('oauth_callback'))

    credentials = OAuth2Credentials.from_json(flask.session['credentials'])
    if credentials.access_token_expired:
        return flask.redirect(flask.url_for('oauth_callback'))
    else:
        http_auth = credentials.authorize(httplib2.Http())
        service = build('calendar', 'v3', http=http_auth)

    try:
        request = service.events().list(calendarId='primary')
        while request is not None:
            response = request.execute()
            for event in response.get('items', []):
                print(repr(event.get('summary', 'NO SUMMARY')) + '\n')
                request = service.events().list_next(request, response)
    except AccessTokenRefreshError:
        print ('The credentials have been revoked or expired, please re-run'
               'the application to re-authorize')

    return 'Hello, World!'


@app.route('/c')
def oauth_callback():
    flow = flow_from_clientsecrets('client_id.json',
                                   scope='https://www.googleapis.com/auth/calendar',
                                   redirect_uri='http://fff9acdd.ngrok.io/c')

    if 'code' not in flask.request.args:
        auth_uri = flow.step1_get_authorize_url()
        return flask.redirect(auth_uri)
    else:
        auth_code = flask.request.args.get('code')
        credentials = flow.step2_exchange(auth_code)
        flask.session['credentials'] = credentials.to_json()
        return flask.redirect(flask.url_for('index'))

    return 'Success'