IdentityServer
IdentityServer is an open-source framework for implementing authentication and authorization in .NET applications using standards like OpenID Connect and OAuth 2.0. It acts as a security token service (STS) that issues tokens to client applications, enabling single sign-on (SSO), API protection, and identity federation across multiple systems. It is commonly used to centralize identity management in microservices architectures and modern web applications.
Developers should learn IdentityServer when building secure .NET applications that require centralized authentication, such as enterprise systems, microservices, or applications with multiple client types (web, mobile, desktop). It is particularly valuable for implementing OAuth 2.0 and OpenID Connect standards to protect APIs, enable single sign-on, and integrate with external identity providers like Azure AD or social logins, reducing custom security code and improving compliance.