Azure Key Vault Storage Account Keys
Before Azure Key Vault Storage Account Keys, developers had to manage their own Azure Storage Account (ASA) keys and rotate them manually or through an external automation. Now, Key Vault Storage Account Keys are implemented as Key Vault secrets for authenticating with an Azure Storage Account.
The Azure Storage Account (ASA) key feature manages secret rotation for you. It also removes the need for your direct contact with an ASA key by offering Shared Access Signatures (SAS) as a method.
For more general information on Azure Storage Accounts, see About Azure storage accounts.
You'll find a complete listing and links to our programming and scripting interfaces in the Key Vault Developer's Guide.
What Key Vault manages
Key Vault performs several internal management functions on your behalf when you use Managed Storage Account Keys.
- Azure Key Vault manages keys of an Azure Storage Account (ASA).
- Internally, Azure Key Vault can list (sync) keys with an Azure Storage Account.
- Azure Key Vault regenerates (rotates) the keys periodically.
- Key values are never returned in response to caller.
- Azure Key Vault manages keys of both Storage Accounts and Classic Storage Accounts.
- Azure Key Vault allows you, the vault/object owner, to create SAS (Shared Access Signature, account or service SAS) definitions.
- The SAS value, created using SAS definition, is returned as a secret via the REST URI path. For more information, see the SAS definition operations in the Azure Key Vault REST API reference.
- Storage account names must be between 3 and 24 characters in length and may contain numbers and lowercase letters only.
- A SAS definition name must be 1-102 characters in length containing only 0-9, a-z, A-Z.
Before Azure Key Vault Storage Keys
Developers used to need to do the following practices with a storage account key to get access to Azure storage.
- Store connection string or SAS token in Azure AppService application settings or another storage.
- At application start-up, fetch the connection string or SAS token.
- Create CloudStorageAccount to interact with storage.
// The Connection string is being fetched from App Service application settings var connectionStringOrSasToken = CloudConfigurationManager.GetSetting("StorageConnectionString"); var storageAccount = CloudStorageAccount.Parse(connectionStringOrSasToken); var blobClient = storageAccount.CreateCloudBlobClient();
After Azure Key Vault Storage Keys
// Create KeyVaultClient with vault credentials var kv = new KeyVaultClient(new KeyVaultClient.AuthenticationCallback(securityToken)); // Get a SAS token for our storage from Key Vault var sasToken = await kv.GetSecretAsync("SecretUri"); // Create new storage credentials using the SAS token. var accountSasCredential = new StorageCredentials(sasToken.Value); // Use the storage credentials and the Blob storage endpoint to create a new Blob service client. var accountWithSas = new CloudStorageAccount(accountSasCredential, new Uri ("https://myaccount.blob.core.windows.net/"), null, null, null); var blobClientWithSas = accountWithSas.CreateCloudBlobClient(); // Use the blobClientWithSas ... // If your SAS token is about to expire, get the SAS Token again from Key Vault and update it. sasToken = await kv.GetSecretAsync("SecretUri"); accountSasCredential.UpdateSASToken(sasToken);
- Only allow Key Vault to manage your ASA keys. Do not attempt to manage them yourself, you will interfere with Key Vault's processes.
- Do not allow ASA keys to be managed by more than one Key Vault object.
- If you need to manually regenerate your ASA keys, we recommend that you regenerate them via Key Vault.
Setup for role-based access control (RBAC) permissions
The Azure Key Vault application identity needs permissions to list and regenerate keys for a storage account. Set up these permissions using the following steps:
# Get the resource ID of the Azure Storage Account you want to manage. # Below, we are fetching a storage account using Azure Resource Manager $storage = Get-AzureRmStorageAccount -ResourceGroupName "mystorageResourceGroup" -StorageAccountName "mystorage" # Get ObjectId of Azure Key Vault Identity $servicePrincipal = Get-AzureRmADServicePrincipal -ServicePrincipalName cfa8b339-82a2-471a-a3c9-0fc0be7a4093 # Assign Storage Key Operator role to Azure Key Vault Identity New-AzureRmRoleAssignment -ObjectId $servicePrincipal.Id -RoleDefinitionName 'Storage Account Key Operator Service Role' -Scope $storage.Id
>[!NOTE] > For a classic account type, set the role parameter to *"Classic Storage Account Key Operator Service Role."*
The following example demonstrates creating a Key Vault managed Azure Storage Account and the associated SAS definitions.
Ensure you have completed Setup for role-based access control (RBAC) permissions.
# This is the name of our Key Vault $keyVaultName = "mykeyVault" # Fetching all the storage account object, of the ASA we want to manage with KeyVault $storage = Get-AzureRmStorageAccount -ResourceGroupName "mystorageResourceGroup" -StorageAccountName "mystorage" # Get ObjectId of Azure KeyVault Identity service principal $servicePrincipalId = $(Get-AzureRmADServicePrincipal -ServicePrincipalName cfa8b339-82a2-471a-a3c9-0fc0be7a4093).Id
Next, set the permissions for your account to ensure that you can manage all the storage permissions in the Key Vault. In the example below, our Azure account is firstname.lastname@example.org_.
# Searching our Azure Active Directory for our account's ObjectId $userPrincipalId = $(Get-AzureRmADUser -SearchString "email@example.com").Id # We use the ObjectId we found to setting permissions on the vault Set-AzureRmKeyVaultAccessPolicy -VaultName $keyVaultName -ObjectId $userPrincipalId -PermissionsToStorage all
Create a Key Vault Managed Storage Account
Now, create a Managed Storage Account in Azure Key Vault and use an access key from your storage account to create the SAS tokens.
-ActiveKeyNameuses 'key2' to generate the SAS tokens.
-AccountNameis used to identify your managed storage account. Below, we are using the storage account name to keep it simple but it can be any name.
-DisableAutoRegenerateKeyspecifies not regenerate the storage account keys.
# Adds your storage account to be managed by Key Vault and will use the access key, key2 Add-AzureKeyVaultManagedStorageAccount -VaultName $keyVaultName -AccountName $storage.StorageAccountName -AccountResourceId $storage.Id -ActiveKeyName key2 -DisableAutoRegenerateKey
If you want Key Vault to regenerate your storage's access keys periodically, you can set a regeneration period. Below, we are setting a regeneration period of 3 days. After 3 days, Key Vault will regenerate 'key1' and swap the active key from 'key2' to 'key1'.
$regenPeriod = [System.Timespan]::FromDays(3) $accountName = $storage.StorageAccountName Add-AzureKeyVaultManagedStorageAccount -VaultName $keyVaultName -AccountName $accountName -AccountResourceId $storage.Id -ActiveKeyName key2 -RegenerationPeriod $regenPeriod
Set SAS definitions
The account SAS provides access to the blob service with different permissions. Set the SAS definitions in Key Vault for your managed storage account.
-AccountNameis the name of the managed storage account in Key Vault.
-Nameis the identifier for the SAS token in your storage.
-ValidityPeriodsets the expiration date for the generated SAS token.
$validityPeriod = [System.Timespan]::FromDays(1) $readSasName = "readBlobSas" $writeSasName = "writeBlobSas" Set-AzureKeyVaultManagedStorageSasDefinition -Service Blob -ResourceType Container,Service -VaultName $keyVaultName -AccountName $accountName -Name $readSasName -Protocol HttpsOnly -ValidityPeriod $validityPeriod -Permission Read,List Set-AzureKeyVaultManagedStorageSasDefinition -Service Blob -ResourceType Container,Service,Object -VaultName $keyVaultName -AccountName $accountName -Name $writeSasName -Protocol HttpsOnly -ValidityPeriod $validityPeriod -Permission Read,List,Write
Get SAS tokens
Get the corresponding SAS tokens and make calls to storage.
constructed using the input from the
Name parameters when
you executed Set-AzureKeyVaultManagedStorageSasDefinition.
$readSasToken = (Get-AzureKeyVaultSecret -VaultName $keyVaultName -SecretName "$accountName-$readSasName").SecretValueText $writeSasToken = (Get-AzureKeyVaultSecret -VaultName $keyVaultName -SecretName "$accountName-$writeSasName").SecretValueText
Notice that trying to access with $readSasToken fails, but that we are able to access with $writeSasToken.
$context1 = New-AzureStorageContext -SasToken $readSasToken -StorageAccountName $storage.StorageAccountName $context2 = New-AzureStorageContext -SasToken $writeSasToken -StorageAccountName $storage.StorageAccountName # Ensure the txt file in command exists in local path mentioned Set-AzureStorageBlobContent -Container containertest1 -File "./abc.txt" -Context $context1 Set-AzureStorageBlobContent -Container cont1-file "./file.txt" -Context $context2
You are able access the storage blob content with the SAS token that has write access.
Relevant Powershell cmdlets
Storage account onboarding
Example: As a Key Vault object owner you add a storage account object to your Azure Key Vault to onboard a storage account.
During onboarding, Key Vault needs to verify that the identity of the onboarding account has permissions to list and to regenerate storage keys. In order to verify these permissions, Key Vault gets an OBO (On Behalf Of) token from the authentication service, audience set to Azure Resource Manager, and makes a list key call to the Azure Storage service. If the list call fails, the Key Vault object creation fails with an HTTP status code of Forbidden. The keys listed in this fashion are cached with your key vault entity storage.
Key Vault must verify that the identity has regenerate permissions before it can take ownership of regenerating your keys. To verify that the identity, via OBO token, as well as the Key Vault first party identity has these permissions:
- Key Vault lists RBAC permissions on the storage account resource.
- Key Vault validates the response via regular expression matching of actions and non-actions.
Find some supporting examples at Key Vault - Managed Storage Account Keys Samples.
If the identity does not have regenerate permissions or if Key Vault's first party identity doesn’t have list or regenerate permission, then the onboarding request fails returning an appropriate error code and message.
The OBO token will only work when you use first-party, native client applications of either PowerShell or CLI.
- SAS tokens, constructed using Key Vault storage account keys, provide even more controlled access to an Azure storage account. For more information, see Using shared access signatures.