Add azure web app identity to Azure Key Vault

gistfile1.txt

{
  "type": "Microsoft.KeyVault/vaults",
  "name": "[variables('keyvault_name')]",
  "apiVersion": "2016-10-01",
  "location": "uksouth",
  "tags": {},
  "scale": null,
  "properties": {
      "sku": {
          "family": "A",
          "name": "Premium"
      },
      "tenantId": "{YOUR_AZURE_AD_TENANT_ID}",
      "accessPolicies": [
          {
              "tenantId": "[reference(concat('Microsoft.Web/sites/', variables('appservice_name')), '2016-08-01', 'Full').identity.tenantId]",
              "objectId": "[reference(concat('Microsoft.Web/sites/', variables('appservice_name')), '2016-08-01', 'Full').identity.principalId]",
              "permissions": {
                  "keys": [
                      "all"
                  ],
                  "secrets": [
                      "all"
                  ]
              }
          }
      ],
      "enabledForDeployment": true,
      "enabledForDiskEncryption": true,
      "enabledForTemplateDeployment": true
  },
  "dependsOn": [
      "[resourceId('Microsoft.Web/sites', variables('appservice_name'))]"
  ]
}