HashiCorp Vault is a centralized secret manager that securely stores and manages sensitive data. It uses a zero-trust security mindset, where identity is the foundational component. In this blog post, the author explains how to achieve user authentication with HashiCorp Vault using OIDC (OpenID Connect) and Microsoft Azure Active Directory (AAD) as a central identity provider. The author demonstrates how AAD can be used to provide identity for users and applications, allowing them to authenticate with Vault without leaking their credentials. The post also discusses the importance of managing secrets and identity in zero-trust security. Additionally, the author provides a Terraform module that registers an application in AAD, making it easier to configure Vault's OIDC auth method using Azure as an identity provider.