mTLS no Webhook PIX com Google Cloud

Bom dia, tudo bem?
Preciso de uma ajuda com o mTLS do webhook pix.
Estamos usando o Google Cloud App Engine para a nossa solução

A documentação oficial diz "SSL support for your App Engine app goes above and beyond basic SSL by offering globally-distributed SSL endpoints and built-in load balancing to serve your app securely, reliably, and quickly to a worldwide audience." (https://cloud.google.com/appengine/docs/standard/nodejs/securing-custom-domains-with-ssl)
E aqui diz "Google Cloud load balancers don't support client certificate-based authentication (mutual TLS, mTLS)." (https://cloud.google.com/load-balancing/docs/ssl-certificates#ssl-certificate-limits)

Voces já solucionaram algum caso parecido? Têm alguma ideia de alternativa? Alguma sugestão doq fazer?

Desde já, muito obrigado 🙂