Custom Environment Support for Azure Auth

[matt14483]

I need to configure Azure Auth to work in a closed Azure Environment, that is not listed in the available configuration options. Since we are adding the Metadata URL during the configuration process anyway, that could be used to configure the environment, rather than the environment parameter. Terraform and Packer are already configured in such a manner to work in these custom Environments.

Packer- https://developer.hashicorp.com/packer/plugins/builders/azure/arm#metadata_host
Terraform- https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs#metadata_host

This would allow me to enable the all the Azure environments at my site to be able to authenticate with Vault, purely based off of subscription and resource group. Other than this, there is no other secure way to automate the use of Vault, without utilizing Azure's KeyVault.