Create custom domain for app services via terraform

I am creating azure app services via terraform and following there documentation located at this site : https://www.terraform.io/docs/providers/azurerm/r/app_service.html

Here is the snippet for terraform script:

resource "azurerm_app_service" "app" {
  name                = "app-name"
  location            = "${azurerm_resource_group.test.location}"
  resource_group_name = "${azurerm_resource_group.test.name}"
  app_service_plan_id = "ommitted"

  site_config {
    java_version           = "1.8"
    java_container         = "TOMCAT"
    java_container_version = "8.5"
  }
  }

I need sub domain as well for my app services for which I am not able to find any help in terraform :

as of now url for app services is: https://abc.azure-custom-domain.cloud

and I want my url to be : https://*.abc.azure-custom-domain.cloud

I know this can be done via portal but is their any way by which we can do it via terraform?

This is not possible. You could the link you provided. If parameter is not in, the parameter is not supported by terraform.

You need do it on Azure Portal.