Azure Active Directory with IdentityServer4 (Microsoft.AspNetCore.Identity.UI) - Step by Step Guide?

Question

I have a .NET Core app which uses identityserver4 to authenticate users. I have integrated it with ASP.NET Identity (Microsoft.AspNetCore.Identity.UI) and this works fine. It uses the AspNetUser tables etc. to store users. etc etc and all the options work.

I would like to add the option to use Azure Active Directory users. So I add the following code to my startup class (previously there was just services.AddAuthentication();):

    services.AddAuthentication()
            .AddOpenIdConnect("aad", "Azure AD", options =>
            {
                options.Authority = "https://login.windows.net/<My Azure Tenant Guid>";
                options.TokenValidationParameters =
                    new TokenValidationParameters { ValidateIssuer = true };
                options.ClientId = "<My Azure App Client Id>";
                options.CallbackPath = "/signin-aad";
                options.SignedOutCallbackPath = "/signout-callback-aad";
                options.RemoteSignOutPath = "/signout-aad";

                options.ResponseType = OpenIdConnectResponseType.Code;

                options.ClientSecret = "<My Azure App Client Secret>";

                options.SignInScheme = IdentityServerConstants.ExternalCookieAuthenticationScheme;
                options.SignOutScheme = IdentityServerConstants.SignoutScheme;
                options.RequireHttpsMetadata = true;
            })
            ;

This makes a button available to add your Azure AD account... Which doesn't work - it gets as far as asking for permission, then comes up with "Unexpected error occurred loading external login info".

Any ideas, or does anyone have a link to a good tutorial?