OAuth2 Google Calendar API Full Example

app.py

import flask
import google.oauth2.credentials
import google_auth_oauthlib.flow
import os
from flask import Flask
from flask import redirect
from flask import request
from googleapiclient.discovery import build

# set up a Flow object that reads the clients from our secrets file with the 
# corresponding scope 
flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(
    'client_secrets.json',
    scopes=['https://www.googleapis.com/auth/calendar'])

# indicate the redirect URI that we placed in the console redirect URI when we 
# created the oauth credentials 
flow.redirect_uri = 'http://localhost:8080/oauth2redirect'

# generates the auth URL that we need to redirect users to where the user 
# gets the oauth consent screen and we get the access code to later exchange for an
# auth token
authorization_url, _ = flow.authorization_url(
    # enables us to grab a refresh token without the user granting us access 
    # a second time if needed
    access_type='offline',
    include_granted_scopes='true')

# create our Flask web app
app = Flask(__name__)

# this allows transport over HTTP for development purposes, if excluded
# HTTPS is needed
os.environ['OAUTHLIB_INSECURE_TRANSPORT'] = '1'

@app.route("/test-api-request")
def test_api_request():
    """Tests an API request to Google Calendar."""
    # grab the credentials from our flask session, in production
    # you will probably store this in some persistent database per user
    credentials = google.oauth2.credentials.Credentials(
      **flask.session['credentials'])

    # build the Google Calendar service which we use to represent the Google Calendar
    # API
    gcal = build('calendar', 'v3', credentials=credentials)
    # grabs Google Calendar events for the particular user who authorized the app
    events_result = gcal.events().list(calendarId='primary',
                                        maxResults=10, singleEvents=True).execute()
    
    # return a JSON response to the front end that shows the results
    return {
        "msg": "successfully processed request",
        "data": events_result
    }

@app.route("/authorize-user")
def auth_user():
    """
    Redirects a user to Google's authorization server to show the OAuth
    Consent screen and get user consent.
    """
    return redirect(authorization_url)

@app.route("/oauth2redirect")
def oauth2_redirect():
    """
    The redirect URI that Google hits after user grants access in the OAuth
    consent screen where we fetch the access token from the access code given in the 
    URL and set them in the flask session.
    """
    # grabs the URL response from the redirect after auth
    authorization_response = request.url

    # fetchs the access code from the request url response
    # and then exchanges it for the token
    flow.fetch_token(authorization_response=authorization_response)

    # grab and set credentials into your flask session 
    # TODO: in production move these credentials to a persistent data store.
    credentials = flow.credentials
    flask.session['credentials'] = {
        'token': credentials.token,
        'refresh_token': credentials.refresh_token,
        'token_uri': credentials.token_uri,
        'client_id': credentials.client_id,
        'client_secret': credentials.client_secret,
        'scopes': credentials.scopes}

    return flask.redirect(flask.url_for('test_api_request'))



if __name__ == "__main__":
    app.secret_key = "development"
    app.run(port=8080, debug=True)