Set properties.webApplicationFirewallConfiguration.enabled attribute to true.

Set waf_configuration.enabled attribute to true.

Example Configuration

resource "azurerm_application_gateway" "allowed" {
  name                = "example474-appgateway"
  resource_group_name = azurerm_resource_group.example474.name
  location            = azurerm_resource_group.example474.location

  waf_configuration {
    enabled             = true
    firewall_mode       = "Prevention"
    rule_set_type       = "OWASP"
    rule_set_version    = "3.0"
  }

  sku {
    name     = "WAF_Medium"
    tier     = "WAF"
    capacity = 2
  }

  gateway_ip_configuration {
    name      = "my-gateway-ip-configuration"
    subnet_id = azurerm_subnet.frontend.id
  }

  frontend_port {
    name = local.frontend_port_name
    port = 80
  }

  frontend_ip_configuration {
    name                 = local.frontend_ip_configuration_name
    public_ip_address_id = azurerm_public_ip.example474.id
  }

  backend_address_pool {
    name = local.backend_address_pool_name
  }

  backend_http_settings {
    name                  = local.http_setting_name
    cookie_based_affinity = "Disabled"
    path                  = "/path1/"
    port                  = 80
    protocol              = "Http"
    request_timeout       = 60
  }

  http_listener {
    name                           = local.listener_name
    frontend_ip_configuration_name = local.frontend_ip_configuration_name
    frontend_port_name             = local.frontend_port_name
    protocol                       = "Http"
  }

  request_routing_rule {
    name                       = local.request_routing_rule_name
    rule_type                  = "Basic"
    http_listener_name         = local.listener_name
    backend_address_pool_name  = local.backend_address_pool_name
    backend_http_settings_name = local.http_setting_name
  }
}