ASP.NET Core Authentication: Schemes, Cookies, JWT, OAuth and OIDC Explained

A detailed technical guide published on DEV Community walks developers through the authentication system in ASP.NET Core, covering its scheme-based, pluggable architecture. The guide explains how every authentication mechanism — whether cookie-based or JWT bearer token — ultimately produces a ClaimsPrincipal that populates HttpContext.User. It covers the two most common authentication approaches: cookie authentication for browser applications and JWT bearer tokens for APIs. The article also clarifies the frequently misunderstood distinction between OAuth 2.0, an authorization delegation protocol, and OpenID Connect, an authentication protocol built on top of it. Additional topics include multi-scheme applications, token validation, refresh tokens, and how authentication integrates with ASP.NET Core's middleware and authorization systems.