Application Security Groups (ASG) support for App Service Environments (ASE)
As stated in the comments section of this page https://azure.microsoft.com/en-us/blog/applicationsecuritygroups/
"It's on the roadmap, all services integrated with VNet like ASE and SQL MI will be part of ASGs groups, as of today the scope doesn't cover subnets for those services, we are exploring options in the near future."
Thank you for the feedback. Our team will evaluate this request and consider it for the future. Please continue to provide feedback/vote on this issue if it is pertinent to your Azure deployment.
Brett, Joe commented
I am also looking for a similar solution with ASG which protects my Azure PaaS services like App Service, Functions. Only accessible from specific network.