Retrieve Azure Key Vault secrets from Logic Apps using Managed Identity

When working with Azure, we should always put our secrets into a secure store, such as Key Vault. This ensures that we can limit who can see the values of our secrets, while still being able to work with them. How we work with these secrets is different over the various services, and in this article we will focus on Logic Apps, while other services will be explained in their own posts later on.

In Logic Apps we often will need some sort of secret, for example a subscription key for API Management, or a SAS key for Event Grid. In the scenario for this blog post we are going to send our secret to a RequestBin endpoint, so we can see that we indeed get the correct value.

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Reference Key Vault secret latest version

NOTE: The explanation below is not officially supported by Microsoft! That said, we have been using this ourselves on several projects, and have seen no issues.

We use Key Vault extensively in our solutions, to store any secrets we might need. For example in an API through code, in Azure Functions via the application settings, or in a Logic App through a REST call. If you go to your secrets in Key Vault, you will notice that the link to the secret includes a version number, in the format of https://kv-we-retrieve-kv-secret.vault.azure.net/secrets/MySecretValue/80df3e46ffcd4f1cb187f79905e9a1e8.

Of course, this is great if we want to reference a specific version of a secret. However, often we will just want to reference the latest version, so we stay up to date even when the secret has been changed, for example because it is a rotating password.

It turns out, this is very easy, without the need to update the version number in all our applications whenever a new version is created. This is done by just omitting the version number from our link! So the will instead look like https://kv-we-retrieve-kv-secret.vault.azure.net/secrets/MySecretValue/.

Important to notice is the trailing slash ( / ), which needs to be included, otherwise you will just get a 404 error.

Retrieve Azure Storage access keys in ARM template

Being a big fan of the Infrastructure as Code (IaC) paradigm, I create all my Azure resources as Azure Resource Manager (ARM) templates. Using an IaC approach, our Azure environments are described as code, allowing us to deploy services in an automated and consistent manner. Often different resources reference other resources, which can introduce the need for authentication. Sometimes we can use Azure Active Directory identities for this (explained more detailed in a later post), however at other times this may require some other form of secrets to set up communication.

Of course, we could create a resource, get the secrets out manually, and then pass them into the referencing resource’s template. However, the idea of Infrastructure as Code, especially when combined with a CI/CD strategy, is to have a minimal amount of manual steps. So instead, let’s have a look at how we can retrieve these secrets from our ARM templates. Consequently, this allows us to set these secrets at deployment time, without any manual interference needed. This article is the first in a series of blog posts, each focusing on a different service, starting with Azure Storage access keys in this post.

Azure Storage Connection String
The connection string which we are going to retrieve
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