Manage HTTPs Request to external load balancer: delay and customise response

[pontorieroa]

Hi,

We have an application behind a global external load balancer and we would like to add a condition, for which if an http request to a specific URL (API of the application behind the load balancer) is sent, then we do something in the background within the application, delaying the response to the API call, then sending a customised JSON response. How can we achieve this in GCP please?

Thanks,