How to Code Sign Your Application with Azure Key Vault

Code Signing with Azure Key Vault: A Practical Guide

Azure Key Vault is a cloud-based vault for your digital keys and certificates. Instead of managing physical USB tokens, everything is centralized, encrypted and accessible only through Azure’s policies. The bonus part is that you can code sign your application directly from Azure via command line.

In this article, we’ll walk through each step, add some practical notes, and share a few tips that make code signing easier.

Why Use Azure Key Vault for Code Signing?

Here are a few reasons how Azure Key Vault improves the code signing process

Instead of manually distributing code signing certificates on physical tokens or local machines, Azure Key Vault stores them in one place, with fine grained access controls.
Certificates and private keys never leave the vault. Even if someone compromises a machine, these files cannot be copied because they don’t exist locally.
Every access and signing request is logged in audit logs. If you ever need to prove who signed what and when, then the audit trail is available.
Whether you’re a solo developer or part of a CI/CD setup with dozens of engineers, Azure integrates nicely with pipelines and permissions.

In practice, many teams move to Azure Key Vault when they start automating builds or distributing software at scale. It reduces the “human factor” risks while giving you control and visibility.

Also Read: What is Azure Key Vault and Why Developers are Adopting it.

Prerequisites for Signing Applications with Azure Key Vault

Before you jump into signing, make sure you’ve got a few things lined up.

Azure Subscription – You’ll need one to create a Key Vault. If you don’t already have one, Azure offers free trial credits that are enough for testing.
Key Vault setup – You can create a Key Vault from the Azure Portal or CLI. It’s a digital locker where certificates are stored.
Code signing certificate – This can come from a Certificate Authority like DigiCert. Some CAs even let you provision certificates directly into Azure. In case your CA doesn’t extend this feature, then you can upload the PFX file to your Key Vault.
Azure CLI – Signing from CLI makes automation easier compared to manual signing. Make sure the signing tool “AzureSignTool” is installed and you’re logged into your Azure account.
Your application file – The .exe, .dll, or installer you want to sign should be ready.

Once you’ve got those pieces, you can move on to setting things up in Key Vault.

Setting Up Azure Key Vault for Code Signing

Create the vault

In the Azure Portal, hit Create a Resource > Security > Key Vault. Give it a name, choose your subscription, and assign a region that is close to your users or build servers.

Set access policies

This is important. Decide who can use the certificate for signing. In a team environment, you’ll want to grant access to your build service principals rather than individuals.

Upload or generate the certificate

If your CA supports it, you can generate the certificate directly in Key Vault. Otherwise, upload your existing PFX along with its password. Azure keeps it safe and ready for signing.

Use role-based access control instead of broad access policies when possible. It makes management easier later when you need to onboard or offboard developers.

Registering an Azure AD Application

For automating access to your Azure Key Vault you’ll need an Azure Active Directory application. This app will act like a secure identity for automated services. You can request certificates using this without exposing sensitive credentials.

Go to Azure Active Directory > App registrations > New registration.
Provide your application with a meaningful name. Provide a redirect URI if required. You’ll receive an Application or Client ID once you register. Keep this handy.
Next, create a client secret by going to Certificates & secrets > New client secret. Give it a description, set an expiration and copy the value immediately. Store this securely as this secret works like a password for your app.
Finally, link your app to the Key Vault. Go to your Key Vault and select Access policies > Add Access Policy. Assign the application the required permissions which are typically Get, Sign, and Verify for certificates. Save your changes.

This setup provides that any automated process like a CI/CD pipeline using AzureSignTool can securely retrieve certificates and sign applications without exposing private keys or requiring manual intervention. It’s a critical step for both security and automation.

Code Signing Using AzureSignTool

The CLI method offers a fast and automated way to sign your applications once your Key Vault and Azure AD application are ready. The recommended tool for this is AzureSignTool. It is a lightweight command line utility that integrates seamlessly with Azure Key Vault.

Install AzureSignTool using the .NET CLI

dotnet tool install --global AzureSignTool

Once the tool is installed then you can sign your application. The key here is connecting securely to your Key Vault using the Application or Client ID and client secret you created.

azuresigntool sign -kvu "<KeyVaultURI>" -kvc "<CertificateName>" -kvi "<ClientID>" -kvs "<ClientSecret>" --azure-key-vault-tenant-id "<TenantID>" -tr http://timestamp.digicert.com -td sha256 "<PathToExecutable>"

Replace the placeholders with your actual values:

<KeyVaultURI> – the URI of your Key Vault
<CertificateName> – the certificate stored in Key Vault
<ClientID> and <ClientSecret> – credentials of your Azure AD app
<TenantID> – your Azure AD tenant ID
<PathToExecutable> – the application file you want to sign

The command not only signs your file but also timestamps it. It guarantees the signature remains valid even after the certificate expires. After signing, verify the signature with

azuresigntool verify "<PathToExecutable>"

The CLI approach is ideal for automation. It makes it perfect for CI/CD pipelines and once configured, your applications can be signed automatically during builds, reducing manual errors and streamlining the deployment process.

Best Practices for Code Signing

Always test your signed file – Sometimes a signature looks fine but isn’t trusted by Windows until you include the right timestamp server. Add -tr http://timestamp.digicert.com -td sha256 to your signtool command so the signature remains valid even when certificate expires.
Use dedicated vaults for production vs. test – Maintain different Key Vaults for development, testing, and production. This reduces the risk of accidentally signing test binaries with production certificates.
Restrict permissions – Only grant signing rights to accounts or services that really need them. Everyone else should have read-only or no access.
Monitor and rotate certificates – Track certificate expiration dates and renew well in advance. Azure can generate alerts to help avoid expired signatures disrupting releases.
Keep logs handy – Turn on Key Vault diagnostics and retain logs in Azure Monitor or Log Analytics. This provides visibility into who accessed certificates and when. It is critical for compliance.

Also Read: The Detailed Guide to Code Signing Certificate Best Practices.

Troubleshooting Common Issues

Even with a smooth setup, a few pitfalls are common

Upload errors: If your PFX upload fails, double-check the password. It’s the most common mistake.
“Key not usable” messages: This usually means you uploaded a certificate without the Extended Key Usage (EKU) flag for Code Signing (OID: 1.3.6.1.5.5.7.3.3). Make sure your CA issued the right type.
Pipeline access issues: If your build server can’t access the vault, check its service principal permissions. Nine times out of ten, it’s an RBAC misconfiguration.
Signature validation fails: Use “signtool verify” with verbose mode. It’ll usually tell you whether it’s a timestamp or certificate trust issue.

Next Steps: Automating and Scaling Your Signing Process

Code signing protects your users, your reputation, and your software integrity. By moving the process into Azure Key Vault, you add a strong layer of security and scalability on top of it. Whether you’re a solo dev distributing a Windows app or part of a team running enterprise pipelines, this approach grows with you. If you haven’t already, start with a testing environment. Upload a certificate, sign a small executable, and verify the results. Once you see how smooth it is, plugging it into your production workflow becomes the natural next step.

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