<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def init_app(self, app):
 """ Do setup that requires a Flask app. :param app: The application to initialize. :type app: Flask """

        secrets = self.load_secrets(app)
        self.client_secrets = list(secrets.values())[0]
        secrets_cache = DummySecretsCache(secrets)

        # Set some default configuration options
        app.config.setdefault('OIDC_SCOPES', ['openid', 'email'])
        app.config.setdefault('OIDC_GOOGLE_APPS_DOMAIN', None)
        app.config.setdefault('OIDC_ID_TOKEN_COOKIE_NAME', 'oidc_id_token')
        app.config.setdefault('OIDC_ID_TOKEN_COOKIE_PATH', '/')
        app.config.setdefault('OIDC_ID_TOKEN_COOKIE_TTL', 7 * 86400)  # 7 days
        # should ONLY be turned off for local debugging
        app.config.setdefault('OIDC_COOKIE_SECURE', True)
        app.config.setdefault('OIDC_VALID_ISSUERS',
                              (self.client_secrets.get('issuer') or
                               GOOGLE_ISSUERS))
        app.config.setdefault('OIDC_CLOCK_SKEW', 60)  # 1 minute
        app.config.setdefault('OIDC_REQUIRE_VERIFIED_EMAIL', False)
        app.config.setdefault('OIDC_OPENID_REALM', None)
        app.config.setdefault('OIDC_USER_INFO_ENABLED', True)
        app.config.setdefault('OIDC_CALLBACK_ROUTE', '/oidc_callback')
        app.config.setdefault('OVERWRITE_REDIRECT_URI', False)
        app.config.setdefault("OIDC_EXTRA_REQUEST_AUTH_PARAMS", {})
        # Configuration for resource servers
        app.config.setdefault('OIDC_RESOURCE_SERVER_ONLY', False)
        app.config.setdefault('OIDC_RESOURCE_CHECK_AUD', False)

        # We use client_secret_post, because that's what the Google
        # oauth2client library defaults to
        app.config.setdefault('OIDC_INTROSPECTION_AUTH_METHOD', 'client_secret_post')
        app.config.setdefault('OIDC_TOKEN_TYPE_HINT', 'access_token')

        if not 'openid' in app.config['OIDC_SCOPES']:
            raise ValueError('The value "openid" must be in the OIDC_SCOPES')

        # register callback route and cookie-setting decorator
        if not app.config['OIDC_RESOURCE_SERVER_ONLY']:
            app.route(app.config['OIDC_CALLBACK_ROUTE'])(self._oidc_callback)
            app.before_request(self._before_request)
            app.after_request(self._after_request)

        # Initialize oauth2client
        self.flow = flow_from_clientsecrets(
            app.config['OIDC_CLIENT_SECRETS'],
            scope=app.config['OIDC_SCOPES'],
            cache=secrets_cache)
        assert isinstance(self.flow, OAuth2WebServerFlow)

        # create signers using the Flask secret key
        self.extra_data_serializer = JSONWebSignatureSerializer(
            app.config['SECRET_KEY'], salt='flask-oidc-extra-data')
        self.cookie_serializer = JSONWebSignatureSerializer(
            app.config['SECRET_KEY'], salt='flask-oidc-cookie')

        try:
            self.credentials_store = app.config['OIDC_CREDENTIALS_STORE']
        except KeyError:
            pass