HashiCorp Vault is a tool for securely storing and managing application secrets and configuration. The article demonstrates how to use HashiCorp Vault with C# .NET to manage application secrets, starting from hardcoding secrets in code to using environment variables and user secrets. It then shows how to persist secrets by running Vault in server mode and using a local file system storage provider. The implementation uses the VaultSharp library to interact with the Vault API. The article concludes that having a centralized, secure system for managing application secrets and configuration is essential, even for development environments.