code: def get_signing_serializer(self, app: 'Quart') -> Optional[URLSafeTimedSerializer]:
          
          if not app.secret_key:
              return None
  
          options = {
              'key_derivation': self.key_derivation,
              'digest_method': self.digest_method,
          }
          return URLSafeTimedSerializer(
              app.secret_key, salt=self.salt, serializer=self.serializer, signer_kwargs=options,
          )
docs: Return a serializer for the session that also signs data.
  
          This will return None if the app is not configured for secrets.