Azure key Vault

The Key Management secrets engine supports lifecycle management of keys in named Azure Key Vault instances. This is accomplished by configuring a KMS provider resource with the azurekeyvault provider and other provider-specific parameter values.

The following sections describe how to properly configure the secrets engine to enable the functionality.

Authentication

The Key Management secrets engine must be configured with credentials that have sufficient permissions to manage keys in an Azure Key Vault instance. The authentication parameters are described in the credentials section of the API documentation. The authentication parameters will be set with the following order of precedence:

If the client ID or secret are not provided and Vault is running on an Azure VM, Vault will attempt to use MSI to access Azure. Note that when MSI is used, the tenant ID must still be explicitly provided by the configuration or environment variable.

An Azure Key Vault access policy determines whether a given service principal, namely an application or user group, can perform certain operations on a Key Vault instance. The service principal associated with the provided credentials must have an access policy on the Key Vault instance with the following minimum key permissions:

Configuration

The following is an example of how to configure the KMS provider resource using the Vault CLI:

$ vault write keymgmt/kms/example-kms \
    provider="azurekeyvault" \
    key_collection="keyvault-name" \
    credentials=client_id="a0454cd1-e28e-405e-bc50-7477fa8a00b7" \
    credentials=client_secret="eR%HizuCVEpAKgeaUEx" \
    credentials=tenant_id="cd4bf224-d114-4f96-9bbc-b8f45751c43f"

Refer to the Azure Key Vault API documentation for a detailed description of individual configuration parameters.

Key transfer specification

Keys are securely transferred from the secrets engine to Azure key vault instances in accordance with the Azure Bring Your Own Key specification.

Key purpose compatibility

The following table defines which key purposes can be used for each key type supported by Azure Key Vault KMS.

Key Type	Purpose
`rsa-2048`	All purposes
`rsa-3072`	All purposes
`rsa-4096`	All purposes

Azure private link

The secrets engine can be configured to communicate with Azure Key Vault instances using Azure Private Endpoints. Follow the guide at Integrate Key Vault with Azure Private Link to set up a Private Endpoint for your target Key Vault instance in Azure. The Private Endpoint must be network reachable by Vault. This means Vault needs to be running in the same virtual network or a peered virtual network to properly resolve the Key Vault domain name to the Private Endpoint IP address.

The Private Endpoint configuration relies on a correct Azure Private DNS integration. From the host that Vault is running on, follow the steps in Validate that the private link connection works to ensure that the Key Vault domain name resolves to the Private Endpoint IP address you've configured.

$ nslookup <keyvault-name>.vault.azure.net
 
Non-authoritative answer:
Name:
Address:  10.0.2.5 (private IP address)
Aliases:  <keyvault-name>.vault.azure.net
          <keyvault-name>.privatelink.vaultcore.azure.net

The secrets engine doesn't require special configuration to communicate with a Key Vault instance over an Azure Private Endpoint. For example, the given KMS configuration will result in the secrets engine resolving a Key Vault domain name of keyvault-name.vault.azure.net to the Private Endpoint IP address. Note that it's possible to change the Key Vault DNS suffix using the environment configuration parameter or AZURE_ENVIRONMENT environment variable.