How to setup Azure App Service to run on .Net Core through Azure Resource Manager

here's how an example web app looks when created from the portal:

{
    "apiVersion": "2018-02-01",
    "name": "[parameters('name')]",
    "type": "Microsoft.Web/sites",
    "location": "[parameters('location')]",
    "properties": {
        "name": "[parameters('name')]",
        "siteConfig": {
            "appSettings": [],
            "metadata": [
                {
                    "name": "CURRENT_STACK",
                    "value": "[parameters('currentStack')]"
                }
            ]
        },
        // redacted some values
    }
},

and the current stack value is dotnetcore