JWT Authentication in ASP.NET Core 10 Web API Using C# – Complete Guide (2026)
A login endpoint is only the beginning of API security. Your application also needs to verify who issued a token, whether it was changed, which API it belongs to, and whether the caller has permission to use an endpoint. This guide explains JWT authentication in ASP.NET Core 10 Web API using C# through a complete local example: a login endpoint, a protected profile endpoint, and an administrator-only endpoint. How does JWT authentication work in ASP.NET Core 10? The client sends an access token in the Authorization: Bearer header. ASP.NET Core's JWT bearer handler validates the token and builds the caller's identity. Authorization policies then decide whether that identity can access the requested endpoint. An invalid or missing token normally produces 401; an authenticated caller without permission receives 403. Important scope: the custom token issuer below is for local development and testing only. It refuses to start outside Development. Microsoft recommends using est...
