Best Practices for Storing Secrets in Azure Key Vault on macOS

Why does the script need to run on your local machine? If you can shift it to Azure—like on a virtual machine or using a function app—you could leverage a managed identity to access the Key Vault without ever exposing the URI. If it must stay local though, I get your concerns about the cert. You might be able to integrate with the macOS keychain after all, but that just means you'd need to manage access to it continually. What's the worst that could happen if someone spams your Teams webhook? Is it really that sensitive?

You could explore using secure strings in PowerShell if that's an option for you. I’m not sure about the capabilities on macOS, but it might help keep your data more secure than just storing certs in plaintext.

Have you considered just allowing the logged-in user to access the Key Vault directly? It might sound too simple, but sometimes over-engineering can lead to more complications than necessary for something that isn't particularly sensitive.

You're thinking in the right direction! Keeping a cert on disk has its own risks, as it essentially becomes another secret to manage. Instead, consider whether you actually need a service principal at all or if a managed identity could simplify things for your macOS tools. That might reduce risk while still granting access to what you need.