What is Azure AD authentication and how does it work with ASP.NET Core?

Azure AD authentication is a way to enable users to sign in to applications and services that are registered in the Azure AD tenant. It provides a centralized authentication and authorization service for cloud and on-premises resources, enabling users to use their organizational account to sign in to different applications and services.

In ASP.NET Core, Azure AD authentication can be easily integrated using the OpenID Connect middleware, which provides support for handling authentication and authorization with Azure AD. The OpenID Connect middleware is responsible for validating tokens, maintaining authentication state, and redirecting users to the Azure AD authentication page.

To enable Azure AD authentication in ASP.NET Core, you need to register your application with Azure AD and configure the OpenID Connect middleware in your application. When a user tries to access a protected resource in your application, the OpenID Connect middleware checks whether the user is authenticated and authorized to access the resource. If the user is not authenticated, the middleware redirects the user to the Azure AD authentication page, where the user can sign in with their organizational account. Once the user is authenticated, the middleware creates an identity for the user and sets an authentication cookie, which is used to maintain authentication state for subsequent requests.

With Azure AD authentication, you can also implement single sign-on (SSO) and single sign-out (SSO), which allows users to sign in to multiple applications and services with a single set of credentials and sign out from all applications and services at once. To enable SSO and SSO, you need to configure your application to use the RemoteSignOutPath property and remove the SameSite attribute from the authentication cookie. SSO and SSO work by setting a hidden iframe to the sign-out URL in Azure AD, which handles the sign-out request.

Additionally, you may also want to consider implementing a revocation endpoint for your application. A revocation endpoint allows a user to revoke their consent for your application to access their data. This can be useful if a user wants to stop using your application or if they no longer want to grant your application access to their data.

To implement a revocation endpoint, you will need to add a route to your ASP.NET Core application that accepts POST requests to a specific URL. When a user revokes consent for your application, your application will receive a POST request to this URL with a token that identifies the user.