if request.method == 'GET':

return render_template('index.html', messages=MESSAGES, tokens=TOKENS,

claims=CLAIMS)

data = request.form.get('payload', 'Example payload').encode('utf-8')

# Consider initializing the publisher client outside this function

# for better latency performance.

publisher = pubsub_v1.PublisherClient()

topic_path = publisher.topic_path(app.config['GOOGLE_CLOUD_PROJECT'],

app.config['PUBSUB_TOPIC'])

future = publisher.publish(topic_path, data)

future.result()

# Verify that the request originates from the application.

if (request.args.get('token', '') !=

current_app.config['PUBSUB_VERIFICATION_TOKEN']):

return 'Invalid request', 400

# Verify that the push request originates from Cloud Pub/Sub.

try:

# Get the Cloud Pub/Sub-generated JWT in the "Authorization" header.

bearer_token = request.headers.get('Authorization')

token = bearer_token.split(' ')[1]

TOKENS.append(token)

# Verify and decode the JWT. `verify_oauth2_token` verifies

# the JWT signature, the `aud` claim, and the `exp` claim.

# Note: For high volume push requests, it would save some network

# overhead if you verify the tokens offline by downloading Google's

# Public Cert and decode them using the `google.auth.jwt` module;

# caching already seen tokens works best when a large volume of

# messages have prompted a single push server to handle them, in which

# case they would all share the same token for a limited time window.

claim = id_token.verify_oauth2_token(token, requests.Request(),

audience='example.com')

# Must also verify the `iss` claim.

if claim['iss'] not in [

'accounts.google.com',

'https://accounts.google.com'

]:

raise ValueError('Wrong issuer.')

CLAIMS.append(claim)

except Exception as e:

return 'Invalid token: {}\n'.format(e), 400

envelope = json.loads(request.data.decode('utf-8'))

payload = base64.b64decode(envelope['message']['data'])

MESSAGES.append(payload)

# Returning any 2xx status indicates successful receipt of the message.

logging.exception('An error occurred during a request.')

return """