Ensure that virtual networks are in use for Azure API Management

Azure API Management should have a virtual network configured to ensure that any backend service access is handled securely.

In Azure Console -

1. Open the Azure Portal and go to API Management.
2. Select the API Management service you wish to edit.
3. Select Network under Deployment + Infrastructure.
4. For Virtual network, choose the appropriate option.
5. Configure the subnet settings as needed.

In Terraform -

1. In the azurerm_api_management resource, set 'virtual_network_type' to [Internal | External].

References:
https://learn.microsoft.com/en-us/azure/api-management/virtual-network-concepts?tabs=stv2
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/api_management#virtual_network_type