What is Blazor? A Tutorial on Building Web Apps with Authentication

I just converted my Azure ASP.Net Web App that uses Auth0 to razor page 3.0 and I’m having troubles with login in. The error I’m getting after I get the Auth0 dialog log is that it can’t find the signin-auth0 url (this used to work). I think my problem is with the end point (I know things have changed in the startup class regarding this). Is there an example that deals with Razor Pages using core 3.0 or 3.1? I definitely want to get to Blazor Server side but want to get the Razor Pages web app working correctly with Auth0 first.
Thanks
John