user_assigned_identity_arm.json

"resources": [
    {
      "apiVersion": "2018-11-01",
      "name": "[parameters('appService_name')]",
      "type": "Microsoft.Web/sites",
      "kind": "WebApp",
      "location": "[parameters('appServicePlan_location')]",
      "identity": {
        "type": "UserAssigned",
        "userAssignedIdentities": {
          "[resourceId('Microsoft.ManagedIdentity/userAssignedIdentities', parameters('appService_identityName'))]": {}
        }
      },
      "tags": {
      },
      "dependsOn": [
      ],
      "resources": [
        {
          "apiVersion": "2018-11-01",
          "name": "MSDeploy",
          "type": "Extensions",
          "dependsOn": [
            "[resourceId('Microsoft.Web/Sites', parameters('appService_name'))]"
          ],
          "properties": {
            "packageUri": "[parameters('servicePackageLink')]"
          }
        }
      ],
      "properties": {
      }
    }
 ]