How to handle JWT in .NET

.NET occupies a distinctive role in the JWT ecosystem, with libraries maintained by Microsoft under the IdentityModel project, seamlessly integrated into ASP.NET Core's authentication pipeline and widely used in applications consuming tokens from Azure AD, Entra ID, or any OIDC-compliant provider. The transition from the legacy JwtSecurityTokenHandler to the modern, more performant JsonWebTokenHandler underscores a significant shift in JWT handling within .NET, which now emphasizes asynchronous operations and improved performance. This guide provides comprehensive insights into both the legacy and modern approaches, covering essential aspects such as token creation, validation, JWKS with automatic key discovery, ASP.NET Core JWT Bearer authentication, claim mapping, and best practices for production environments. It highlights the importance of using modern libraries for better security and performance, configuring JWT handling through the Authority pattern for OIDC providers, and adopting practices like policy-based authorization and short-lived tokens for enhanced security. Additionally, WorkOS is presented as a solution for managing enterprise authentication needs, offering a .NET SDK to streamline OAuth flows and support features like Single Sign-On and user management without the need for building an entire authentication stack from scratch.