Azure Key Vault is a Microsoft cloud service for securely storing and managing secrets, keys and certificates. Applications retrieve passwords, API keys, connection strings and TLS certificates through URIs instead of keeping them in code. The service comes in a Standard tier using software cryptography and a Premium tier with keys protected in hardware security modules (HSMs). Key Vault is delivered as a managed service within Azure.
Microsoft is a US company, so US legislation such as the CLOUD Act may apply to keys stored in Azure. A vault is created in a single Azure region of your choice, including European regions, and is replicated to a paired region within the same geography. According to Microsoft, the service is designed so that Microsoft does not see or extract your data. For data protection, Microsoft refers to its Data Protection Addendum. The service is not open source. Organisations that want key management under their own jurisdiction can assess whether a vault in a US provider's cloud meets that requirement.