Ensure Web Application Firewall(WAF) is enabled for Azure Application Gateway

Disabled WAF keeps applications in Azure Application Gateway open to all layer 7 attacks.

In Azure Console -

1. Log into portal, go to Azure marketplace.
2. Search for Application Gateway.
3. Select it, click create.
4. Follow rest of the prompts and configure as needed.

In Terraform -

1. In the azurerm_application_gateway resource, configure 'waf_configuration' block as needed.

References:
https://learn.microsoft.com/en-us/azure/web-application-firewall/ag/ag-overview
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/application_gateway#waf_configuration