Create a user delegation SAS for a container or blob with PowerShell (preview)

A shared access signature (SAS) enables you to grant limited access to containers and blobs in your storage account. When you create a SAS, you specify its constraints, including which Azure Storage resources a client is allowed to access, what permissions they have on those resources, and how long the SAS is valid.

Every SAS is signed with a key. You can sign a SAS in one of two ways:

  • With a key created using Azure Active Directory (Azure AD) credentials. A SAS signed with Azure AD credentials is a user delegation SAS.
  • With the storage account key. Both a service SAS and an account SAS are signed with the storage account key.

This article shows how to use Azure Active Directory (Azure AD) credentials to create a user delegation SAS for a container or blob with Azure PowerShell (preview).

About the user delegation SAS (preview)

A SAS token for access to a container or blob may be secured by using either Azure AD credentials or an account key. A SAS secured with Azure AD credentials is called a user delegation SAS, because the OAuth 2.0 token used to sign the SAS is requested on behalf of the user.

Microsoft recommends that you use Azure AD credentials when possible as a security best practice, rather than using the account key, which can be more easily compromised. When your application design requires shared access signatures, use Azure AD credentials to create a user delegation SAS for superior security. For more information about the user delegation SAS, see Create a user delegation SAS.

Note

The user delegation SAS preview is intended for non-production use only.

Caution

Any client that possesses a valid SAS can access data in your storage account as permitted by that SAS. It's important to protect a SAS from malicious or unintended use. Use discretion in distributing a SAS, and have a plan in place for revoking a compromised SAS.

For more information about shared access signatures, see Grant limited access to Azure Storage resources using shared access signatures (SAS).

Install the preview module

To use PowerShell to create a user delegation SAS, you must first install the Az.Storage 1.3.1-preview module. Follow these steps to install the module:

  1. Uninstall any previous installations of Azure PowerShell:

    • Remove any previous installations of Azure PowerShell from Windows using the Apps & features setting under Settings.
    • Remove all Azure modules from %Program Files%\WindowsPowerShell\Modules.
  2. Make sure that you have the latest version of PowerShellGet installed. Open a Windows PowerShell window, and run the following command to install the latest version:

    Install-Module PowerShellGet –Repository PSGallery –Force
    
  3. Close and reopen the PowerShell window after installing PowerShellGet.

  4. Install the latest version of Azure PowerShell:

    Install-Module Az –Repository PSGallery –AllowClobber
    
  5. Install an Azure Storage preview module that supports user delegation SAS:

    Install-Module Az.Storage `
        –Repository PSGallery `
        -RequiredVersion 1.3.1-preview `
        –AllowPrerelease `
        –AllowClobber `
        –Force
    
  6. Close and reopen the PowerShell window.

Because PowerShell loads the latest Az.Storage module by default, you may need to explicitly load the 1.3.1-preview module when you start the console. To explicitly load the preview module, run the Import-Module command:

Import-Module Az.Storage -RequiredVersion 1.3.1

For more information about installing Azure PowerShell, see Install Azure PowerShell with PowerShellGet.

Sign in to Azure PowerShell with Azure AD

Call the Connect-AzAccount command to sign in with your Azure AD account:

Connect-AzAccount

For more information about signing in with PowerShell, see Sign in with Azure PowerShell.

Assign permissions with RBAC

To create a user delegation SAS from Azure PowerShell, the Azure AD account used to sign into PowerShell must be assigned a role that includes the Microsoft.Storage/storageAccounts/blobServices/generateUserDelegationKey action. This permission enables that Azure AD account to request the user delegation key. The user delegation key is used to sign the user delegation SAS. The role providing the Microsoft.Storage/storageAccounts/blobServices/generateUserDelegationKey action must be assigned at the level of the storage account, the resource group, or the subscription. For more information about RBAC permissions for creating a user delegation SAS, see the Assign permissions with RBAC section in Create a user delegation SAS.

If you do not have sufficient permissions to assign RBAC roles to an Azure AD security principal, you may need to ask the account owner or administrator to assign the necessary permissions.

The following example assigns the Storage Blob Data Contributor role, which includes the Microsoft.Storage/storageAccounts/blobServices/generateUserDelegationKey action. The role is scoped at the level of the storage account.

Remember to replace placeholder values in angle brackets with your own values:

New-AzRoleAssignment -SignInName <email> `
    -RoleDefinitionName "Storage Blob Data Contributor" `
    -Scope  "/subscriptions/<subscription>/resourceGroups/<resource-group>/providers/Microsoft.Storage/storageAccounts/<storage-account>"

For more information about the built-in roles that include the Microsoft.Storage/storageAccounts/blobServices/generateUserDelegationKey action, see Built-in roles for Azure resources.

Use Azure AD credentials to secure a SAS

When you create a user delegation SAS with Azure PowerShell, the user delegation key that is used to sign the SAS is created for you implicitly. The start time and expiry time that you specify for the SAS are also used as the start time and expiry time for the user delegation key.

Because the maximum interval over which the user delegation key is valid is 7 days from the start date, you should specify an expiry time for the SAS that is within 7 days of the start time. The SAS is invalid after the user delegation key expires, so a SAS with an expiry time of greater than 7 days will still only be valid for 7 days.

To create a user delegation SAS for a container or blob with Azure PowerShell, first create a new Azure Storage context object, specifying the -UseConnectedAccount parameter. The -UseConnectedAccount parameter specifies that the command creates the context object under the Azure AD account with which you signed in.

Remember to replace placeholder values in angle brackets with your own values:

$ctx = New-AzStorageContext -StorageAccountName <storage-account> -UseConnectedAccount

Create a user delegation SAS for a container

To return a user delegation SAS token for a container, call the New-AzStorageContainerSASToken command, passing in the Azure Storage context object that you created previously.

The following example returns a user delegation SAS token for a container. Remember to replace the placeholder values in brackets with your own values:

New-AzStorageContainerSASToken -Context $ctx `
    -Name <container> `
    -Permission racwdl `
    -ExpiryTime <date-time>

The user delegation SAS token returned will be similar to:

?sv=2018-11-09&sr=c&sig=<sig>&skoid=<skoid>&sktid=<sktid>&skt=2019-08-05T22%3A24%3A36Z&ske=2019-08-07T07%3A
00%3A00Z&sks=b&skv=2018-11-09&se=2019-08-07T07%3A00%3A00Z&sp=rwdl

Create a user delegation SAS for a blob

To return a user delegation SAS token for a blob, call the New-AzStorageBlobSASToken command, passing in the Azure Storage context object that you created previously.

The following syntax returns a user delegation SAS for a blob. The example specifies the -FullUri parameter, which returns the blob URI with the SAS token appended. Remember to replace the placeholder values in brackets with your own values:

New-AzStorageBlobSASToken -Context $ctx `
    -Container <container> `
    -Blob <blob> `
    -Permission racwd `
    -ExpiryTime <date-time>
    -FullUri

The user delegation SAS URI returned will be similar to:

https://storagesamples.blob.core.windows.net/sample-container/blob1.txt?sv=2018-11-09&sr=b&sig=<sig>&skoid=<skoid>&sktid=<sktid>&skt=2019-08-06T21%3A16%3A54Z&ske=2019-08-07T07%3A00%3A00Z&sks=b&skv=2018-11-09&se=2019-08-07T07%3A00%3A00Z&sp=racwd

Note

A user delegation SAS does not support defining permissions with a stored access policy.

Revoke a user delegation SAS

To revoke a user delegation SAS from Azure PowerShell, call the Revoke-AzStorageAccountUserDelegationKeys command. This command revokes all of the user delegation keys associated with the specified storage account. Any shared access signatures associated with those keys are invalidated.

Remember to replace placeholder values in angle brackets with your own values:

Revoke-AzStorageAccountUserDelegationKeys -ResourceGroupName <resource-group> `
    -StorageAccountName <storage-account>

Important

Both the user delegation key and RBAC role assignments are cached by Azure Storage, so there may be a delay between when you initiate the process of revocation and when an existing user delegation SAS becomes invalid.

Next steps