Duende Identity Server is an OpenID Connect and OAuth 2.0 framework for ASP.NET Core. Duende Identity Server enables the following security features:
* Authentication as a Service (AaaS)
* Single sign-on/off (SSO) over multiple application types
* Access control for APIs
* Federation Gateway
> [!IMPORTANT]
> [Duende Software](https://duendesoftware.com/) might require you to pay a license fee for production use of Duende Identity Server. For more information, see <xref:migration/50-to-60#project-templates-use-duende-identity-server>.
For more information, see the [Duende Identity Server documentation (Duende Software website)](https://docs.duendesoftware.com).