Manage storage account keys with Key Vault and Azure PowerShell (legacy)

Important

Key Vault Managed Storage Account Keys (legacy) is supported as-is with no more updates planned. Only Account SAS are supported with SAS definitions signed storage service version no later than 2018-03-28.

Important

We recommend using Azure Storage integration with Azure Active Directory (Azure AD), Microsoft's cloud-based identity and access management service. Azure AD integration is available for Azure blobs and queues, and provides OAuth2 token-based access to Azure Storage (just like Azure Key Vault). Azure AD allows you to authenticate your client application by using an application or user identity, instead of storage account credentials. You can use an Azure AD managed identity when you run on Azure. Managed identities remove the need for client authentication and storing credentials in or with your application. Use below solution only when Azure AD authentication is not possible.

An Azure storage account uses credentials comprising an account name and a key. The key is autogenerated and serves as a password, rather than an as a cryptographic key. Key Vault manages storage account keys by periodically regenerating them in storage account and provides shared access signature tokens for delegated access to resources in your storage account.

You can use the Key Vault managed storage account key feature to list (sync) keys with an Azure storage account, and regenerate (rotate) the keys periodically. You can manage keys for both storage accounts and Classic storage accounts.

When you use the managed storage account key feature, consider the following points:

  • Key values are never returned in response to a caller.
  • Only Key Vault should manage your storage account keys. Don't manage the keys yourself and avoid interfering with Key Vault processes.
  • Only a single Key Vault object should manage storage account keys. Don't allow key management from multiple objects.
  • Regenerate keys by using Key Vault only. Don't manually regenerate your storage account keys.

Important

Regenerating key directly in storage account breaks managed storage account setup and can invalidate SAS tokens in use and cause an outage.

Note

We recommend that you use the Azure Az PowerShell module to interact with Azure. See Install Azure PowerShell to get started. To learn how to migrate to the Az PowerShell module, see Migrate Azure PowerShell from AzureRM to Az.

Service principal application ID

An Azure AD tenant provides each registered application with a service principal. The service principal serves as the application ID, which is used during authorization setup for access to other Azure resources via Azure RBAC.

Key Vault is a Microsoft application that's pre-registered in all Azure AD tenants. Key Vault is registered under the same Application ID in each Azure cloud.

Tenants Cloud Application ID
Azure AD Azure Government 7e7c393b-45d0-48b1-a35e-2905ddf8183c
Azure AD Azure public cfa8b339-82a2-471a-a3c9-0fc0be7a4093
Other Any cfa8b339-82a2-471a-a3c9-0fc0be7a4093

Prerequisites

To complete this guide, you must first do the following:

Manage storage account keys

Connect to your Azure account

Authenticate your PowerShell session using the Connect-AzAccount cmdlet.

Connect-AzAccount

If you have multiple Azure subscriptions, you can list them using the Get-AzSubscription cmdlet, and specify the subscription you wish to use with the Set-AzContext cmdlet.

Set-AzContext -SubscriptionId <subscriptionId>

Set variables

First, set the variables to be used by the PowerShell cmdlets in the following steps. Be sure to update the "YourResourceGroupName", "YourStorageAccountName", and "YourKeyVaultName" placeholders, and set $keyVaultSpAppId to cfa8b339-82a2-471a-a3c9-0fc0be7a4093 (as specified in Service principal application ID, above).

We will also use the Azure PowerShell Get-AzContext and Get-AzStorageAccount cmdlets to get your user ID and the context of your Azure storage account.

$resourceGroupName = <YourResourceGroupName>
$storageAccountName = <YourStorageAccountName>
$keyVaultName = <YourKeyVaultName>
$keyVaultSpAppId = "cfa8b339-82a2-471a-a3c9-0fc0be7a4093"
$storageAccountKey = "key1" #(key1 or key2 are allowed)

# Get your User Id
$userId = (Get-AzContext).Account.Id

# Get a reference to your Azure storage account
$storageAccount = Get-AzStorageAccount -ResourceGroupName $resourceGroupName -StorageAccountName $storageAccountName

Note

For Classic Storage Account use "primary" and "secondary" for $storageAccountKey
Use 'Get-AzResource -Name "ClassicStorageAccountName" -ResourceGroupName $resourceGroupName' instead of'Get-AzStorageAccount' for Classic Storage Account

Give Key Vault access to your storage account

Before Key Vault can access and manage your storage account keys, you must authorize its access your storage account. The Key Vault application requires permissions to list and regenerate keys for your storage account. These permissions are enabled through the Azure built-in role Storage Account Key Operator Service Role.

Assign this role to the Key Vault service principal, limiting scope to your storage account, using the Azure PowerShell New-AzRoleAssignment cmdlet.

# Assign Azure role "Storage Account Key Operator Service Role" to Key Vault, limiting the access scope to your storage account. For a classic storage account, use "Classic Storage Account Key Operator Service Role."
New-AzRoleAssignment -ApplicationId $keyVaultSpAppId -RoleDefinitionName 'Storage Account Key Operator Service Role' -Scope $storageAccount.Id

Upon successful role assignment, you should see output similar to the following example:

RoleAssignmentId   : /subscriptions/03f0blll-ce69-483a-a092-d06ea46dfb8z/resourceGroups/rgContoso/providers/Microsoft.Storage/storageAccounts/sacontoso/providers/Microsoft.Authorization/roleAssignments/189cblll-12fb-406e-8699-4eef8b2b9ecz
Scope              : /subscriptions/03f0blll-ce69-483a-a092-d06ea46dfb8z/resourceGroups/rgContoso/providers/Microsoft.Storage/storageAccounts/sacontoso
DisplayName        : Azure Key Vault
SignInName         :
RoleDefinitionName : storage account Key Operator Service Role
RoleDefinitionId   : 81a9662b-bebf-436f-a333-f67b29880f12
ObjectId           : 93c27d83-f79b-4cb2-8dd4-4aa716542e74
ObjectType         : ServicePrincipal
CanDelegate        : False

If Key Vault has already been added to the role on your storage account, you'll receive a "The role assignment already exists." error. You can also verify the role assignment, using the storage account "Access control (IAM)" page in the Azure portal.

Give your user account permission to managed storage accounts

Use the Azure PowerShell Set-AzKeyVaultAccessPolicy cmdlet to update the Key Vault access policy and grant storage account permissions to your user account.

# Give your user principal access to all storage account permissions, on your Key Vault instance

Set-AzKeyVaultAccessPolicy -VaultName $keyVaultName -UserPrincipalName $userId -PermissionsToStorage get, list, delete, set, update, regeneratekey, getsas, listsas, deletesas, setsas, recover, backup, restore, purge

Note that permissions for storage accounts aren't available on the storage account "Access policies" page in the Azure portal.

Add a managed storage account to your Key Vault instance

Use the Azure PowerShell Add-AzKeyVaultManagedStorageAccount cmdlet to create a managed storage account in your Key Vault instance. The -DisableAutoRegenerateKey switch specifies NOT to regenerate the storage account keys.

# Add your storage account to your Key Vault's managed storage accounts

Add-AzKeyVaultManagedStorageAccount -VaultName $keyVaultName -AccountName $storageAccountName -AccountResourceId $storageAccount.Id -ActiveKeyName $storageAccountKey -DisableAutoRegenerateKey

Upon successful addition of the storage account with no key regeneration, you should see output similar to the following example:

Id                  : https://kvcontoso.vault.azure.net:443/storage/sacontoso
Vault Name          : kvcontoso
AccountName         : sacontoso
Account Resource Id : /subscriptions/03f0blll-ce69-483a-a092-d06ea46dfb8z/resourceGroups/rgContoso/providers/Microsoft.Storage/storageAccounts/sacontoso
Active Key Name     : key1
Auto Regenerate Key : False
Regeneration Period : 90.00:00:00
Enabled             : True
Created             : 11/19/2018 11:54:47 PM
Updated             : 11/19/2018 11:54:47 PM
Tags                :

Enable key regeneration

If you want Key Vault to regenerate your storage account keys periodically, you can use the Azure PowerShell Add-AzKeyVaultManagedStorageAccount cmdlet to set a regeneration period. In this example, we set a regeneration period of thirty days. When it is time to rotate, Key Vault regenerates the key that is not active, and then sets the newly created key as active. Only one of the keys are used to issue SAS tokens at any one time. This is the active key.

$regenPeriod = [System.Timespan]::FromDays(30)

Add-AzKeyVaultManagedStorageAccount -VaultName $keyVaultName -AccountName $storageAccountName -AccountResourceId $storageAccount.Id -ActiveKeyName $storageAccountKey -RegenerationPeriod $regenPeriod

Upon successful addition of the storage account with key regeneration, you should see output similar to the following example:

Id                  : https://kvcontoso.vault.azure.net:443/storage/sacontoso
Vault Name          : kvcontoso
AccountName         : sacontoso
Account Resource Id : /subscriptions/03f0blll-ce69-483a-a092-d06ea46dfb8z/resourceGroups/rgContoso/providers/Microsoft.Storage/storageAccounts/sacontoso
Active Key Name     : key1
Auto Regenerate Key : True
Regeneration Period : 30.00:00:00
Enabled             : True
Created             : 11/19/2018 11:54:47 PM
Updated             : 11/19/2018 11:54:47 PM
Tags                :

Shared access signature tokens

You can also ask Key Vault to generate shared access signature tokens. A shared access signature provides delegated access to resources in your storage account. You can grant clients access to resources in your storage account without sharing your account keys. A shared access signature provides you with a secure way to share your storage resources without compromising your account keys.

The commands in this section complete the following actions:

  • Set an account shared access signature definition.
  • Set a Key Vault managed storage shared access signature definition in the vault. The definition has the template URI of the shared access signature token that was created. The definition has the shared access signature type account and is valid for N days.
  • Verify that the shared access signature was saved in your key vault as a secret.

Set variables

First, set the variables to be used by the PowerShell cmdlets in the following steps. Be sure to update the <YourStorageAccountName> and <YourKeyVaultName> placeholders.

We will also use the Azure PowerShell New-AzStorageContext cmdlets to get the context of your Azure storage account.

$storageAccountName = <YourStorageAccountName>
$keyVaultName = <YourKeyVaultName>

$storageContext = New-AzStorageContext -StorageAccountName $storageAccountName -Protocol Https -StorageAccountKey Key1 #(or "Primary" for Classic Storage Account)

Define a shared access signature definition template

Key Vault uses SAS definition template to generate tokens for client applications.

SAS definition template example:

$sasTemplate="sv=2018-03-28&ss=bfqt&srt=sco&sp=rw&spr=https"

Account SAS parameters required in SAS definition template for Key Vault

SAS Query Parameter Description
SignedVersion (sv) Required. Specifies the signed storage service version to use to authorize requests made with this account SAS. Must be set to version 2015-04-05 or later. Key Vault supports versions no later than 2018-03-28
SignedServices (ss) Required. Specifies the signed services accessible with the account SAS. Possible values include:

- Blob (b)
- Queue (q)
- Table (t)
- File (f)

You can combine values to provide access to more than one service. For example, ss=bf specifies access to the Blob and File endpoints.
SignedResourceTypes (srt) Required. Specifies the signed resource types that are accessible with the account SAS.

- Service (s): Access to service-level APIs (e.g., Get/Set Service Properties, Get Service Stats, List Containers/Queues/Tables/Shares)
- Container (c): Access to container-level APIs (e.g., Create/Delete Container, Create/Delete Queue, Create/Delete Table, Create/Delete Share, List Blobs/Files and Directories)
- Object (o): Access to object-level APIs for blobs, queue messages, table entities, and files(e.g. Put Blob, Query Entity, Get Messages, Create File, etc.)

You can combine values to provide access to more than one resource type. For example, srt=sc specifies access to service and container resources.
SignedPermission (sp) Required. Specifies the signed permissions for the account SAS. Permissions are only valid if they match the specified signed resource type; otherwise they are ignored.

- Read (r): Valid for all signed resources types (Service, Container, and Object). Permits read permissions to the specified resource type.
- Write (w): Valid for all signed resources types (Service, Container, and Object). Permits write permissions to the specified resource type.
- Delete (d): Valid for Container and Object resource types, except for queue messages.
- Permanent Delete (y): Valid for Object resource type of Blob only.
- List (l): Valid for Service and Container resource types only.
- Add (a): Valid for the following Object resource types only: queue messages, table entities, and append blobs.
- Create (c): Valid for the following Object resource types only: blobs and files. Users can create new blobs or files, but may not overwrite existing blobs or files.
- Update (u): Valid for the following Object resource types only: queue messages and table entities.
- Process (p): Valid for the following Object resource type only: queue messages.
- Tag (t): Valid for the following Object resource type only: blobs. Permits blob tag operations.
- Filter (f): Valid for the following Object resource type only: blob. Permits filtering by blob tag.
- Set Immutability Policy (i): Valid for the following Object resource type only: blob. Permits set/delete immutability policy and legal hold on a blob.
SignedProtocol (spr) Optional. Specifies the protocol permitted for a request made with the account SAS. Possible values are both HTTPS and HTTP (https,http) or HTTPS only (https). The default value is https,http.

Note that HTTP only is not a permitted value.

For more information about account SAS, see: Create an account SAS

Note

Key Vault ignores lifetime parameters like 'Signed Expiry', 'Signed Start' and parameters introduced after 2018-03-28 version

Set shared access signature definition in Key Vault

Use the the Azure PowerShell Set-AzKeyVaultManagedStorageSasDefinition cmdlet to create a shared access signature definition. You can provide the name of your choice to the -Name parameter.

Set-AzKeyVaultManagedStorageSasDefinition -AccountName $storageAccountName -VaultName $keyVaultName -Name <YourSASDefinitionName> -TemplateUri $sasTemplate -SasType 'account' -ValidityPeriod ([System.Timespan]::FromDays(1))

Verify the shared access signature definition

You can verify that the shared access signature definition has been stored in your key vault using the Azure PowerShell Get-AzKeyVaultSecret cmdlet.

First, find the shared access signature definition in your key vault.

Get-AzKeyVaultSecret -VaultName <YourKeyVaultName>

The secret corresponding to your SAS definition will have these properties:

Vault Name   : <YourKeyVaultName>
Name         : <SecretName>
...
Content Type : application/vnd.ms-sastoken-storage
Tags         :

You can now use the Get-AzKeyVaultSecret cmdlet with the VaultName and Name parameters to view the contents of that secret.

$secretValueText = Get-AzKeyVaultSecret -VaultName <YourKeyVaultName> -Name <SecretName> -AsPlainText
Write-Output $secretValueText

The output of this command will show your SAS definition string.

Next steps