code: def init_config(self, app):
          
          config_apps = ['APP_', 'RATELIMIT_']
          flask_talisman_debug_mode = ["'unsafe-inline'"]
          for k in dir(config):
              if any([k.startswith(prefix) for prefix in config_apps]):
                  app.config.setdefault(k, getattr(config, k))
  
          if app.config['DEBUG']:
              app.config.setdefault('APP_DEFAULT_SECURE_HEADERS', {})
              headers = app.config['APP_DEFAULT_SECURE_HEADERS']
              # ensure `content_security_policy` is not set to {}
              if headers.get('content_security_policy') != {}:
                  headers.setdefault('content_security_policy', {})
                  csp = headers['content_security_policy']
                  # ensure `default-src` is not set to []
                  if csp.get('default-src') != []:
                      csp.setdefault('default-src', [])
                      # add default `content_security_policy` value when debug
                      csp['default-src'] += flask_talisman_debug_mode
docs: Initialize configuration.
  
          :param app: An instance of :class:`~flask.Flask`.