Add vault azure secret backend role

[petems]

Now #481 is merged, now lets create the role for azure secrets! 😄

This one's a bit trickier to test, as it requires real subscription information...

So for the test you'll require the following environment variables:

ARM_TENANT_ID
ARM_CLIENT_ID
ARM_CLIENT_SECRET
ARM_RESOURCE_GROUP

The resource group you can create with the CLI, or use an existing one if needed:

az group create --name 'azure-vault-tf-testing' && export ARM_RESOURCE_GROUP="azure-vault-tf-testing"

So, you'll need to create a service principal, then enable the permissions to create new accounts from that account, which is only possible with Powershell 😭 (so you have to do it from the Azure Cloud Shell)

Doc to do that: https://www.terraform.io/docs/providers/azuread/auth/service_principal_configuration.html

[petems]

From my personal testing with my setup:

resource "vault_azure_secret_backend" "azure" {
	subscription_id = "<REDACTED>"
	tenant_id = "<REDACTED>"
	client_id = "<REDACTED>"
	client_secret = "<REDACTED>"
}

resource "vault_azure_secret_backend_role" "test" {
  backend                     = "${vault_azure_secret_backend.azure.path}"
  role                        = "test"
  ttl                         = 300
	max_ttl                   = 600
	description				  = "Test for Vault Provider"

	azure_roles {
    role_name = "Reader"
    scope =  "/subscriptions/<REDACTED>/resourceGroups/psouter-vault-secret-azure-backend"
  }
}

$ 2019-08-07T22:23:09.490+0100 [INFO]  core: successful mount: namespace= path=azure/ type=azure

$ vault list azure/roles
Keys
----
test

$ vault read azure/creds/test
Key                Value
---                -----
lease_id           azure/creds/test/[...]
[...]

[petems]

To remind myself, the full CLI command I ran was:

envchain azure ENV ARM_RESOURCE_GROUP=psouter-vault-secret-azure-backend TF_ACC=1 go test -timeout 30s github.com/terraform-providers/terraform-provider-vault/vault -run '^(TestAzureSecretBackendRole)$' -v

[tyrannosaurus-becks]

This looks fantastic! Just a couple minor tweaks needed with the Description and path, and it'll be good to go.

[tyrannosaurus-becks]

🌈 Thank you!