I have found many different solutions with OAuth and either with some libraries or with pure requests (<https://github.com/googlesamples/oauth-apps-for-windows>).

However, none of the solutions looks like the one that I really need. Currently, my application uses its own database for users to log in using WCF service request (with username and password). However, all users have their domain e-mail created with Google accounts, so I want to add another button "Sign In with Google", which will just make sure that user can also login with his Google e-mail-password pair. I don't need a returned token for the further use etc.

What is the simplest way to achieve this functionality in WPF/C# desktop application?