Refresh token

Using the sample tenant provided I am able to get an access token and a refresh token.

The access token expires in one hour and the refresh token in 14 days.

If I try to open the Tasks page after the access token has expired, I am redirected to the b2clogin page, and a completely new access and refresh token are being retrieved.

This sounds different than what I expect after [reading this](https://github.com/AzureAD/microsoft-authentication-library-for-dotnet/issues/1811#issuecomment-627310839).

I am expecting AcquireTokenSilent to use the refresh token to retrieve a new access token in the background.

Let me know if this is a problem with the sample or an issue with the [library](https://github.com/AzureAD/microsoft-authentication-library-for-dotnet).