Hi Alessandro. Thanks for reading and I also saw your question on stack overflow (which is closed).

Anyway, https load balancer has only routing feature and not security/filtering feature. Therefore, you can add API Key check and management on the load balancer.

However, in a near future, you will be able to add an API Gateway as serverless NEG backend of a load balancer. Thus, you will be able to use the routing capacity of Load balancer to route your request to API Gateway, and then to perform your API Key check on API Gateway and to forward the request to the corresponding Cloud Run.

Note: API Gateway and Cloud Run + ESPv2 are the same, except that API Gateway is a fully manage service.