Three Ways to Implement API Key Authentication in ASP.NET Core on .NET 9

A tutorial from DEV Community demonstrates three approaches to API key authentication in ASP.NET Core running on .NET 9. The methods covered are middleware for app-wide protection, an MVC authorization filter for controller-level control, and an endpoint filter for minimal API routes. All three approaches read the header name and secret key from configuration using the Options pattern, binding values to a typed class rather than loose strings. Developers are advised to store actual key values in a secret store such as Azure Key Vault or environment variables in production, never in appsettings.json. The guide also highlights a common pitfall in endpoint filters where failing to return immediately after a 401 response causes the pipeline to continue unintentionally.