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IdentityServer is an open-source OpenID Connect and OAuth 2.0 framework for ASP.NET Core that’s especially favored in the dev community. IdentityServer4 (IS4) became the de facto standard for.NET-based token services. Now it serves as a central authentication server for thousands of apps that allows creating a robust authentication & authorization system within the projects. Starting November 2022, the service will undergo drastic changes - Rebranding.