IdentityModel is a collection of OpenID Connect & OAuth 2 related helpers and client libraries for .NET and ASP.NET.
The main repos are
- IdentityModel - core library containing primitives and basic interactions with protocol endpoints
- IdentityModel.AspNetCore.OAuth2Introspection - Implementation of an OAuth 2 token introspection client for ASP.NET Core
- IdentityModel.OidcClient - RFC8252 compliant client library for native clients
IdentityModel is maintained by Duende Software.
See here for documentation.