Create an ASP.NET Office Add-in that uses single sign-on (preview)
When users are signed in to Office, your add-in can use the same credentials to permit users to access multiple applications without requiring them to sign in a second time. For an overview, see Enable SSO in an Office Add-in.
There has been a recent change in the SSO APIs. We are working on a new walkthrough that explains how to create an add-in that uses SSO and that is built with ASP.NET, OWIN, and Microsoft Authentication Library (MSAL) for .NET. In the meantime, see the complete sample at Office Add-in ASPNET SSO.