docs: def init_app(self, app):
          """Initializes an application for using :class:`docker.Client`.
  
          :param app: an instance of :class:`~flask.Flask`.
          """
          app.extensions = getattr(app, 'extensions', {})
          app.extensions['docker.client'] = None
  
          app.config.setdefault('DOCKER_URL', None)
          app.config.setdefault('DOCKER_VERSION', '1.16')
          app.config.setdefault('DOCKER_TIMEOUT', 30)
          app.config.setdefault('DOCKER_TLS', False)
          app.config.setdefault('DOCKER_TLS_VERIFY', True)
          app.config.setdefault('DOCKER_TLS_SSL_VERSION', None)
          app.config.setdefault('DOCKER_TLS_ASSERT_HOSTNAME', None)
  
          app.config.setdefault('DOCKER_TLS_CERT_PATH', None)
          app.config.setdefault('DOCKER_TLS_CLIENT_CERT', None)
          app.config.setdefault('DOCKER_TLS_CA_CERT', None)