low-level Oauth2 flask example

Taken from http://bitwiser.in/2015/09/09/add-google-login-in-flask.html

Setup

1. Follow these instructions to create CLIENT_ID and CLIENT_SECRET

   or just use ready ones in app.py.

2. open CMD, go to project root and type (Windows)

virtualenv env
env\Scripts\activate.bat

pip install -r requirements.txt

3. Then run app:

python app.py