provider/azurerm: add client_config data source

azurerm_client_config provides access to:

 - client_id
 - tenant_id
 - subscription_id

```
TF_ACC=1 go test ./builtin/providers/azurerm -v -run TestAccAzureRMClientConfig -timeout 120m
=== RUN   TestAccAzureRMClientConfig_basic
--- PASS: TestAccAzureRMClientConfig_basic (27.79s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/azurerm	27.862s
```

builtin/providers/azurerm/config.go

@@ -24,6 +24,10 @@ import (
 // ArmClient contains the handles to all the specific Azure Resource Manager
 // resource classes' respective clients.
 type ArmClient struct {
+	clientId       string
+	tenantId       string
+	subscriptionId string
+
 	rivieraClient *riviera.Client
 
 	availSetClient         compute.AvailabilitySetsClient
@@ -110,7 +114,11 @@ func setUserAgent(client *autorest.Client) {
 // *ArmClient based on the Config's current settings.
 func (c *Config) getArmClient() (*ArmClient, error) {
 	// client declarations:
-	client := ArmClient{}
+	client := ArmClient{
+		clientId:       c.ClientID,
+		tenantId:       c.TenantID,
+		subscriptionId: c.SubscriptionID,
+	}
 
 	rivieraClient, err := riviera.NewClient(&riviera.AzureResourceManagerCredentials{
 		ClientID:       c.ClientID,

builtin/providers/azurerm/data_source_arm_client_config.go

@@ -0,0 +1,39 @@
+package azurerm
+
+import (
+	"time"
+
+	"github.com/hashicorp/terraform/helper/schema"
+)
+
+func dataSourceArmClientConfig() *schema.Resource {
+	return &schema.Resource{
+		Read: dataSourceArmClientConfigRead,
+
+		Schema: map[string]*schema.Schema{
+			"client_id": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"tenant_id": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"subscription_id": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+		},
+	}
+}
+
+func dataSourceArmClientConfigRead(d *schema.ResourceData, meta interface{}) error {
+	client := meta.(*ArmClient)
+
+	d.SetId(time.Now().UTC().String())
+	d.Set("client_id", client.clientId)
+	d.Set("tenant_id", client.tenantId)
+	d.Set("subscription_id", client.subscriptionId)
+
+	return nil
+}

builtin/providers/azurerm/data_source_arm_client_config_test.go

@@ -0,0 +1,48 @@
+package azurerm
+
+import (
+	"os"
+	"testing"
+
+	"github.com/hashicorp/terraform/helper/resource"
+	"github.com/hashicorp/terraform/terraform"
+)
+
+func TestAccAzureRMClientConfig_basic(t *testing.T) {
+	clientId := os.Getenv("ARM_CLIENT_ID")
+	tenantId := os.Getenv("ARM_TENANT_ID")
+	subscriptionId := os.Getenv("ARM_SUBSCRIPTION_ID")
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:  func() { testAccPreCheck(t) },
+		Providers: testAccProviders,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccCheckArmClientConfig_basic,
+				Check: resource.ComposeTestCheckFunc(
+					testAzureRMClientConfigAttr("data.azurerm_client_config.current", "client_id", clientId),
+					testAzureRMClientConfigAttr("data.azurerm_client_config.current", "tenant_id", tenantId),
+					testAzureRMClientConfigAttr("data.azurerm_client_config.current", "subscription_id", subscriptionId),
+				),
+			},
+		},
+	})
+}
+
+// Wraps resource.TestCheckResourceAttr to prevent leaking values to console
+// in case of mismatch
+func testAzureRMClientConfigAttr(name, key, value string) resource.TestCheckFunc {
+	return func(s *terraform.State) error {
+		err := resource.TestCheckResourceAttr(name, key, value)(s)
+		if err != nil {
+			// return fmt.Errorf("%s: Attribute '%s', failed check (values hidden)", name, key)
+			return err
+		}
+
+		return nil
+	}
+}
+
+const testAccCheckArmClientConfig_basic = `
+data "azurerm_client_config" "current" { }
+`

builtin/providers/azurerm/provider.go

@@ -44,6 +44,10 @@ func Provider() terraform.ResourceProvider {
 			},
 		},
 
+		DataSourcesMap: map[string]*schema.Resource{
+			"azurerm_client_config": dataSourceArmClientConfig(),
+		},
+
 		ResourcesMap: map[string]*schema.Resource{
 			// These resources use the Azure ARM SDK
 			"azurerm_availability_set": resourceArmAvailabilitySet(),

website/source/docs/providers/azurerm/d/client_config.html.markdown

@@ -0,0 +1,31 @@
+---
+layout: "azurerm"
+page_title: "Azure Resource Manager: azurerm_client_config"
+sidebar_current: "docs-azurerm-datasource-client-config"
+description: |-
+  Get information about the configuration of the azurerm provider.
+---
+
+# azurerm\_client\_config
+
+Use this data source to access the configuration 
+
+## Example Usage
+
+```
+data "azurerm_client_config" "current" { }
+
+output "account_id" {
+  value = "${data.azurerm_client_config.current.account_id}"
+}
+```
+
+## Argument Reference
+
+There are no arguments available for this data source.
+
+## Attributes Reference
+
+`client_id` is set to the Azure Client ID. 
+`tenant_id` is set to the Azure Tenant ID.
+`subscription_id` is set to the Azure Subscription ID. 

website/source/layouts/azurerm.erb

@@ -11,6 +11,15 @@
               <a href="/docs/providers/azurerm/index.html">Microsoft Azure Provider</a>
             </li>
 
+            <li<%= sidebar_current(/^docs-azurerm-datasource/) %>>
+              <a href="#">Data Sources</a>
+              <ul class="nav nav-visible">
+                <li<%= sidebar_current("docs-azurerm-datasource-client-config-") %>>
+                    <a href="/docs/providers/aws/d/client_config.html">azurerm_client_config</a>
+                </li>
+              </ul>
+            </li>
+
             <li<%= sidebar_current(/^docs-azurerm-resource-resource/) %>>
               <a href="#">Base Resources</a>
               <ul class="nav nav-visible">