backend/azurerm: support for authenticating via SAS Tokens (#19440)

* adding acceptance tests for msi auth

* including the resource group name in the tests

* backend/azurerm: support for authenticating using a SAS Token

* resolving merge conflicts

* moving the defer to prior to the error

backend/remote-state/azure/arm_client.go

@@ -3,7 +3,10 @@ package azure
 import (
 	"context"
 	"fmt"
+	"log"
+	"net/url"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/Azure/azure-sdk-for-go/profiles/2017-03-09/resources/mgmt/resources"
@@ -25,6 +28,7 @@ type ArmClient struct {
 	environment        azure.Environment
 	resourceGroupName  string
 	storageAccountName string
+	sasToken           string
 }
 
 func buildArmClient(config BackendConfig) (*ArmClient, error) {
@@ -44,6 +48,12 @@ func buildArmClient(config BackendConfig) (*ArmClient, error) {
 		return &client, nil
 	}
 
+	// likewise with a SAS token
+	if config.SasToken != "" {
+		client.sasToken = config.SasToken
+		return &client, nil
+	}
+
 	builder := authentication.Builder{
 		ClientID:       config.ClientID,
 		ClientSecret:   config.ClientSecret,
@@ -85,6 +95,7 @@ func buildArmClient(config BackendConfig) (*ArmClient, error) {
 
 func (c ArmClient) getBlobClient(ctx context.Context) (*storage.BlobStorageClient, error) {
 	if c.accessKey != "" {
+		log.Printf("Building the Blob Client from an Access Token")
 		storageClient, err := storage.NewBasicClientOnSovereignCloud(c.storageAccountName, c.accessKey, c.environment)
 		if err != nil {
 			return nil, fmt.Errorf("Error creating storage client for storage account %q: %s", c.storageAccountName, err)
@@ -93,6 +104,20 @@ func (c ArmClient) getBlobClient(ctx context.Context) (*storage.BlobStorageClien
 		return &client, nil
 	}
 
+	if c.sasToken != "" {
+		log.Printf("Building the Blob Client from a SAS Token")
+		token := strings.TrimPrefix(c.sasToken, "?")
+		uri, err := url.ParseQuery(token)
+		if err != nil {
+			return nil, fmt.Errorf("Error parsing SAS Token: %+v", err)
+		}
+
+		storageClient := storage.NewAccountSASClient(c.storageAccountName, uri, c.environment)
+		client := storageClient.GetBlobService()
+		return &client, nil
+	}
+
+	log.Printf("Building the Blob Client from an Access Token (using user credentials)")
 	keys, err := c.storageAccountsClient.ListKeys(ctx, c.resourceGroupName, c.storageAccountName)
 	if err != nil {
 		return nil, fmt.Errorf("Error retrieving keys for Storage Account %q: %s", c.storageAccountName, err)

backend/remote-state/azure/backend.go

@@ -44,6 +44,13 @@ func New() backend.Backend {
 				DefaultFunc: schema.EnvDefaultFunc("ARM_ACCESS_KEY", ""),
 			},
 
+			"sas_token": {
+				Type:        schema.TypeString,
+				Optional:    true,
+				Description: "A SAS Token used to interact with the Blob Storage Account.",
+				DefaultFunc: schema.EnvDefaultFunc("ARM_SAS_TOKEN", ""),
+			},
+
 			"resource_group_name": {
 				Type:        schema.TypeString,
 				Optional:    true,
@@ -122,6 +129,7 @@ type BackendConfig struct {
 	Environment       string
 	MsiEndpoint       string
 	ResourceGroupName string
+	SasToken          string
 	SubscriptionID    string
 	TenantID          string
 	UseMsi            bool
@@ -145,6 +153,7 @@ func (b *Backend) configure(ctx context.Context) error {
 		Environment:        data.Get("environment").(string),
 		MsiEndpoint:        data.Get("msi_endpoint").(string),
 		ResourceGroupName:  data.Get("resource_group_name").(string),
+		SasToken:           data.Get("sas_token").(string),
 		StorageAccountName: data.Get("storage_account_name").(string),
 		SubscriptionID:     data.Get("arm_subscription_id").(string),
 		TenantID:           data.Get("arm_tenant_id").(string),
@@ -156,8 +165,8 @@ func (b *Backend) configure(ctx context.Context) error {
 		return err
 	}
 
-	if config.AccessKey == "" && config.ResourceGroupName == "" {
+	if config.AccessKey == "" && config.SasToken == "" && config.ResourceGroupName == "" {
-		return fmt.Errorf("Either an Access Key or the Resource Group for the Storage Account must be specified")
+		return fmt.Errorf("Either an Access Key / SAS Token or the Resource Group for the Storage Account must be specified")
 	}
 
 	b.armClient = armClient

backend/remote-state/azure/backend_test.go

@@ -43,17 +43,18 @@ func TestBackendAccessKeyBasic(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
 		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
 		"container_name":       res.storageContainerName,
 		"key":                  res.storageKeyName,
 		"access_key":           res.storageAccountAccessKey,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
 	})).(*Backend)
 
 	backend.TestBackendStates(t, b)
@@ -67,11 +68,10 @@ func TestBackendManagedServiceIdentityBasic(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
@@ -87,6 +87,35 @@ func TestBackendManagedServiceIdentityBasic(t *testing.T) {
 	backend.TestBackendStates(t, b)
 }
 
+func TestBackendSASTokenBasic(t *testing.T) {
+	testAccAzureBackend(t)
+	rs := acctest.RandString(4)
+	res := testResourceNames(rs, "testState")
+	armClient := buildTestClient(t, res)
+
+	ctx := context.TODO()
+	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
+	if err != nil {
+		t.Fatalf("Error creating Test Resources: %q", err)
+	}
+
+	sasToken, err := buildSasToken(res.storageAccountName, res.storageAccountAccessKey)
+	if err != nil {
+		t.Fatalf("Error building SAS Token: %+v", err)
+	}
+
+	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
+		"storage_account_name": res.storageAccountName,
+		"container_name":       res.storageContainerName,
+		"key":                  res.storageKeyName,
+		"sas_token":            *sasToken,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
+	})).(*Backend)
+
+	backend.TestBackendStates(t, b)
+}
+
 func TestBackendServicePrincipalBasic(t *testing.T) {
 	testAccAzureBackend(t)
 	rs := acctest.RandString(4)
@@ -95,11 +124,10 @@ func TestBackendServicePrincipalBasic(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
@@ -124,17 +152,17 @@ func TestBackendAccessKeyLocked(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b1 := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
 		"container_name":       res.storageContainerName,
 		"key":                  res.storageKeyName,
 		"access_key":           res.storageAccountAccessKey,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
 	})).(*Backend)
 
 	b2 := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
@@ -142,6 +170,7 @@ func TestBackendAccessKeyLocked(t *testing.T) {
 		"container_name":       res.storageContainerName,
 		"key":                  res.storageKeyName,
 		"access_key":           res.storageAccountAccessKey,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
 	})).(*Backend)
 
 	backend.TestBackendStateLocks(t, b1, b2)
@@ -156,11 +185,10 @@ func TestBackendServicePrincipalLocked(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b1 := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,

backend/remote-state/azure/client_test.go

@@ -24,17 +24,17 @@ func TestRemoteClientAccessKeyBasic(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
 		"container_name":       res.storageContainerName,
 		"key":                  res.storageKeyName,
 		"access_key":           res.storageAccountAccessKey,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
 	})).(*Backend)
 
 	state, err := b.StateMgr(backend.DefaultStateName)
@@ -53,11 +53,10 @@ func TestRemoteClientManagedServiceIdentityBasic(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
@@ -78,6 +77,40 @@ func TestRemoteClientManagedServiceIdentityBasic(t *testing.T) {
 	remote.TestClient(t, state.(*remote.State).Client)
 }
 
+func TestRemoteClientSasTokenBasic(t *testing.T) {
+	testAccAzureBackend(t)
+	rs := acctest.RandString(4)
+	res := testResourceNames(rs, "testState")
+	armClient := buildTestClient(t, res)
+
+	ctx := context.TODO()
+	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
+	if err != nil {
+		t.Fatalf("Error creating Test Resources: %q", err)
+	}
+
+	sasToken, err := buildSasToken(res.storageAccountName, res.storageAccountAccessKey)
+	if err != nil {
+		t.Fatalf("Error building SAS Token: %+v", err)
+	}
+
+	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
+		"storage_account_name": res.storageAccountName,
+		"container_name":       res.storageContainerName,
+		"key":                  res.storageKeyName,
+		"sas_token":            *sasToken,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
+	})).(*Backend)
+
+	state, err := b.StateMgr(backend.DefaultStateName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	remote.TestClient(t, state.(*remote.State).Client)
+}
+
 func TestRemoteClientServicePrincipalBasic(t *testing.T) {
 	testAccAzureBackend(t)
 	rs := acctest.RandString(4)
@@ -86,11 +119,10 @@ func TestRemoteClientServicePrincipalBasic(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
@@ -120,17 +152,17 @@ func TestRemoteClientAccessKeyLocks(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b1 := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
 		"container_name":       res.storageContainerName,
 		"key":                  res.storageKeyName,
 		"access_key":           res.storageAccountAccessKey,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
 	})).(*Backend)
 
 	b2 := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
@@ -138,6 +170,7 @@ func TestRemoteClientAccessKeyLocks(t *testing.T) {
 		"container_name":       res.storageContainerName,
 		"key":                  res.storageKeyName,
 		"access_key":           res.storageAccountAccessKey,
+		"environment":          os.Getenv("ARM_ENVIRONMENT"),
 	})).(*Backend)
 
 	s1, err := b1.StateMgr(backend.DefaultStateName)
@@ -161,11 +194,10 @@ func TestRemoteClientServicePrincipalLocks(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	b1 := backend.TestBackendConfig(t, New(), backend.TestWrapConfig(map[string]interface{}{
 		"storage_account_name": res.storageAccountName,
@@ -212,11 +244,10 @@ func TestPutMaintainsMetaData(t *testing.T) {
 
 	ctx := context.TODO()
 	err := armClient.buildTestResources(ctx, &res)
+	defer armClient.destroyTestResources(ctx, res)
 	if err != nil {
-		armClient.destroyTestResources(ctx, res)
 		t.Fatalf("Error creating Test Resources: %q", err)
 	}
-	defer armClient.destroyTestResources(ctx, res)
 
 	headerName := "acceptancetest"
 	expectedValue := "f3b56bad-33ad-4b93-a600-7a66e9cbd1eb"

backend/remote-state/azure/helpers_test.go

@@ -7,10 +7,16 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/Azure/azure-sdk-for-go/profiles/2017-03-09/resources/mgmt/resources"
 	armStorage "github.com/Azure/azure-sdk-for-go/profiles/2017-03-09/storage/mgmt/storage"
 	"github.com/Azure/azure-sdk-for-go/storage"
+	sasStorage "github.com/hashicorp/go-azure-helpers/storage"
+)
+
+const (
+	sasSignedVersion = "2017-07-29"
 )
 
 // verify that we are doing ACC tests or the Azure tests specifically
@@ -80,6 +86,31 @@ func buildTestClient(t *testing.T, res resourceNames) *ArmClient {
 	return armClient
 }
 
+func buildSasToken(accountName, accessKey string) (*string, error) {
+	// grant full access to Objects in the Blob Storage Account
+	permissions := "rwdlacup" // full control
+	resourceTypes := "sco"    // service, container, object
+	services := "b"           // blob
+
+	// Details on how to do this are here:
+	// https://docs.microsoft.com/en-us/rest/api/storageservices/Constructing-an-Account-SAS
+	signedProtocol := "https,http"
+	signedIp := ""
+	signedVersion := sasSignedVersion
+
+	utcNow := time.Now().UTC()
+	startDate := utcNow.Format(time.RFC3339)
+	endDate := utcNow.Add(time.Hour * 24).Format(time.RFC3339)
+
+	sasToken, err := sasStorage.ComputeSASToken(accountName, accessKey, permissions, services, resourceTypes,
+		startDate, endDate, signedProtocol, signedIp, signedVersion)
+	if err != nil {
+		return nil, fmt.Errorf("Error computing SAS Token: %+v", err)
+	}
+	log.Printf("SAS Token should be %q", sasToken)
+	return &sasToken, nil
+}
+
 type resourceNames struct {
 	resourceGroup           string
 	location                string

go.mod

@@ -55,7 +55,7 @@ require (
 	github.com/grpc-ecosystem/grpc-gateway v1.5.1 // indirect
 	github.com/hashicorp/consul v0.0.0-20171026175957-610f3c86a089
 	github.com/hashicorp/errwrap v1.0.0
-	github.com/hashicorp/go-azure-helpers v0.0.0-20181120094008-dd1e326c8888
+	github.com/hashicorp/go-azure-helpers v0.0.0-20181122151743-c51a3103be3b
 	github.com/hashicorp/go-checkpoint v0.0.0-20171009173528-1545e56e46de
 	github.com/hashicorp/go-cleanhttp v0.5.0
 	github.com/hashicorp/go-getter v0.0.0-20180327010114-90bb99a48d86

go.sum

@@ -124,6 +124,8 @@ github.com/hashicorp/errwrap v1.0.0 h1:hLrqtEDnRye3+sgx6z4qVLNuviH3MR5aQ0ykNJa/U
 github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-azure-helpers v0.0.0-20181120094008-dd1e326c8888 h1:QdenIfqH8llhlVDlGQWVUhg+L8pDT9VteOlMstWRl+w=
 github.com/hashicorp/go-azure-helpers v0.0.0-20181120094008-dd1e326c8888/go.mod h1:e+GPy2nvD+spqsdjUyw5tbo73rBbu955QBaV9GZoBEA=
+github.com/hashicorp/go-azure-helpers v0.0.0-20181122151743-c51a3103be3b h1:AJjRaIeZiWlhYVf2skNYOjooaaIOcQzS94a3iSKnXKE=
+github.com/hashicorp/go-azure-helpers v0.0.0-20181122151743-c51a3103be3b/go.mod h1:e+GPy2nvD+spqsdjUyw5tbo73rBbu955QBaV9GZoBEA=
 github.com/hashicorp/go-checkpoint v0.0.0-20171009173528-1545e56e46de h1:XDCSythtg8aWSRSO29uwhgh7b127fWr+m5SemqjSUL8=
 github.com/hashicorp/go-checkpoint v0.0.0-20171009173528-1545e56e46de/go.mod h1:xIwEieBHERyEvaeKF/TcHh1Hu+lxPM+n2vT1+g9I4m4=
 github.com/hashicorp/go-cleanhttp v0.5.0 h1:wvCrVc9TjDls6+YGAF2hAifE1E5U1+b4tH6KdvN3Gig=

vendor/github.com/hashicorp/go-azure-helpers/storage/sas_token.go

@@ -0,0 +1,98 @@
+package storage
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"fmt"
+	"net/url"
+	"strings"
+)
+
+const (
+	connStringAccountKeyKey  = "AccountKey"
+	connStringAccountNameKey = "AccountName"
+)
+
+// ComputeSASToken computes the SAS Token for a Storage Account based on the
+// access key & given permissions
+func ComputeSASToken(accountName string,
+	accountKey string,
+	permissions string,
+	services string,
+	resourceTypes string,
+	start string,
+	expiry string,
+	signedProtocol string,
+	signedIp string, // nolint: unparam
+	signedVersion string, // nolint: unparam
+) (string, error) {
+
+	// UTF-8 by default...
+	stringToSign := accountName + "\n"
+	stringToSign += permissions + "\n"
+	stringToSign += services + "\n"
+	stringToSign += resourceTypes + "\n"
+	stringToSign += start + "\n"
+	stringToSign += expiry + "\n"
+	stringToSign += signedIp + "\n"
+	stringToSign += signedProtocol + "\n"
+	stringToSign += signedVersion + "\n"
+
+	binaryKey, err := base64.StdEncoding.DecodeString(accountKey)
+	if err != nil {
+		return "", err
+	}
+	hasher := hmac.New(sha256.New, binaryKey)
+	hasher.Write([]byte(stringToSign))
+	signature := hasher.Sum(nil)
+
+	// Trial and error to determine which fields the Azure portal
+	// URL encodes for a query string and which it does not.
+	sasToken := "?sv=" + url.QueryEscape(signedVersion)
+	sasToken += "&ss=" + url.QueryEscape(services)
+	sasToken += "&srt=" + url.QueryEscape(resourceTypes)
+	sasToken += "&sp=" + url.QueryEscape(permissions)
+	sasToken += "&se=" + (expiry)
+	sasToken += "&st=" + (start)
+	sasToken += "&spr=" + (signedProtocol)
+
+	// this is consistent with how the Azure portal builds these.
+	if len(signedIp) > 0 {
+		sasToken += "&sip=" + signedIp
+	}
+
+	sasToken += "&sig=" + url.QueryEscape(base64.StdEncoding.EncodeToString(signature))
+
+	return sasToken, nil
+}
+
+// ParseStorageAccountConnectionString parses the Connection String for a Storage Account
+func ParseStorageAccountConnectionString(connString string) (map[string]string, error) {
+	// This connection string was for a real storage account which has been deleted
+	// so its safe to include here for reference to understand the format.
+	// DefaultEndpointsProtocol=https;AccountName=azurermtestsa0;AccountKey=2vJrjEyL4re2nxCEg590wJUUC7PiqqrDHjAN5RU304FNUQieiEwS2bfp83O0v28iSfWjvYhkGmjYQAdd9x+6nw==;EndpointSuffix=core.windows.net
+	validKeys := map[string]bool{"DefaultEndpointsProtocol": true, "BlobEndpoint": true,
+		"AccountName": true, "AccountKey": true, "EndpointSuffix": true}
+	// The k-v pairs are separated with semi-colons
+	tokens := strings.Split(connString, ";")
+
+	kvp := make(map[string]string)
+
+	for _, atoken := range tokens {
+		// The individual k-v are separated by an equals sign.
+		kv := strings.SplitN(atoken, "=", 2)
+		key := kv[0]
+		val := kv[1]
+		if _, present := validKeys[key]; !present {
+			return nil, fmt.Errorf("[ERROR] Unknown Key: %s", key)
+		}
+		kvp[key] = val
+	}
+
+	if _, present := kvp[connStringAccountKeyKey]; !present {
+		return nil, fmt.Errorf("[ERROR] Storage Account Key not found in connection string: %s", connString)
+	}
+
+	return kvp, nil
+}

vendor/modules.txt

@@ -302,8 +302,9 @@ github.com/hashicorp/consul/lib/freeport
 github.com/hashicorp/consul/testutil/retry
 # github.com/hashicorp/errwrap v1.0.0
 github.com/hashicorp/errwrap
-# github.com/hashicorp/go-azure-helpers v0.0.0-20181120094008-dd1e326c8888
+# github.com/hashicorp/go-azure-helpers v0.0.0-20181122151743-c51a3103be3b
 github.com/hashicorp/go-azure-helpers/authentication
+github.com/hashicorp/go-azure-helpers/storage
 # github.com/hashicorp/go-checkpoint v0.0.0-20171009173528-1545e56e46de
 github.com/hashicorp/go-checkpoint
 # github.com/hashicorp/go-cleanhttp v0.5.0

website/docs/backends/types/azurerm.html.md

@@ -58,6 +58,22 @@ terraform {
 }
 ```
 
+When authenticating using a SAS Token associated with the Storage Account:
+
+```hcl
+terraform {
+  backend "azurerm" {
+    storage_account_name = "abcd1234"
+    container_name       = "tfstate"
+    key                  = "prod.terraform.tfstate"
+
+    # rather than defining this inline, the SAS Token can also be sourced
+    # from an Environment Variable - more information is available below.
+    sas_token = "abcdefghijklmnopqrstuvwxyz0123456789..."
+  }
+}
+```
+
 -> **NOTE:** When using a Service Principal or an Access Key - we recommend using a [Partial Configuration](/docs/backends/config.html) for the credentials.
 
 ## Example Referencing
@@ -106,6 +122,22 @@ data "terraform_remote_state" "foo" {
     access_key = "abcdefghijklmnopqrstuvwxyz0123456789..."
   }
 }
+
+When authenticating using a SAS Token associated with the Storage Account:
+
+```hcl
+data "terraform_remote_state" "foo" {
+  backend = "azurerm"
+  config = {
+    storage_account_name = "terraform123abc"
+    container_name       = "terraform-state"
+    key                  = "prod.terraform.tfstate"
+
+    # rather than defining this inline, the SAS Token can also be sourced
+    # from an Environment Variable - more information is available below.
+    sas_token = "abcdefghijklmnopqrstuvwxyz0123456789..."
+  }
+}
 ```
 
 ## Configuration variables
@@ -134,6 +166,12 @@ When authenticating using the Managed Service Identity (MSI) - the following fie
 
 ---
 
+When authenticating using a SAS Token associated with the Storage Account - the following fields are also supported:
+
+* `sas_token` - (Optional) The SAS Token used to access the Blob Storage Account. This can also be sourced from the `ARM_SAS_TOKEN` environment variable.
+
+---
+
 When authenticating using the Storage Account's Access Key - the following fields are also supported:
 
 * `access_key` - (Optional) The Access Key used to access the Blob Storage Account. This can also be sourced from the `ARM_ACCESS_KEY` environment variable.