A Key Vault is a service that allows us to safely store certificates or secrets and later use them in our applications and services. And like many other Azure services it has a cost but it’s really low and, for a normal use, you will be billed like a cent or none a month. Don’t be stingy with security! You might already know about Azure Key Vault because we can use it in Microsoft Dynamics 365 for Finance and Operations under System Administration. For example it’s how the company certificates for the Spanish SII or Brazilian NF-e are stored and later retrieved to call the web services.