Auth0.ExcelAddin | sample VSTO Excel Add-in that authenticates users

Auth0.ExcelAddin is a C# library. Auth0.ExcelAddin has no bugs, it has no vulnerabilities, it has a Permissive License and it has low support. You can download it from GitHub.

This sample demonstrates how to build a VSTO Excel 2016 add-in (C#). This sample creates a Ribbon with a single button. When the user clicks the button a web browser will open redirecting the user the /authiorize endpoint. Once the user completes login the code and code verifier will be returned and exchanged for tokens. This sample uses Auth0 as an authentication and authorization server using Authorization Code Grant Flow with PKCE. A special note about Excel. If you are migrating from the legacy (deprecated) SDK Auth0.WinformsOrWPF there is a significant breaking change. In Excel the System.Threading.SynchronizationContext.Current is set to null. With the old SDK this was not problematic. However, in the new SDK Auth0.OidcClient.WinForms takes on a dependency to IdentityModel.OidcClient2. This SDK does a lot asynchronous calls with await/async and utilizes ConfigureAwait(false). At some point the SDK makes a call to System.Net.Http.HttpClient.GetUrl(string). This class is thread safe and when used will run on a new thread in a mutli-tenant apartment. After the call is made .NET will look to see if the SynchronizationContext is not null and use that for swithing the current thread. If .NET finds this as null it falls back to using the ThreadScheduler. In the case of ThreadScheduler the remaining method calls will continue on the MTA thread. Eventually the method attempts to invoke the WebBrowser object and this fails, because it requies to be invoked in a single-threaded apartment. The following example solves this by setting up a SynchronizationContext before invoking login.