App Service web app has a managed identity configured

# Enable system-assigned managed identity on the App Service app (use azurerm_linux_web_app or azurerm_windows_web_app)
resource "azurerm_linux_web_app" "<example_resource_name>" {
  name                = "<example_resource_name>"
  location            = azurerm_resource_group.<example_resource_name>.location
  resource_group_name = azurerm_resource_group.<example_resource_name>.name
  service_plan_id     = azurerm_service_plan.<example_resource_name>.id

  site_config {}

  identity {                    # Critical: enables managed identity
    type = "SystemAssigned"    # Creates a system-assigned identity for the app
  }
}

// Enable system-assigned managed identity on an existing App Service app
resource app 'Microsoft.Web/sites@2022-09-01' = {
  name: '<example_resource_name>'
  location: resourceGroup().location
  identity: {
    type: 'SystemAssigned' // Critical: enables a managed identity for the app
  }
}