How to access a service added to DI container from inside Asp.Net Core's ConfigureServices method

Question

The code sample below is from Asp.Net Core ConfigureServices method in Startup.cs.

I am first registering a singleton service called AppState. Subsequent to that, I am configuring OpenIdConnect, and inside the OnTokenValidated lambda, I need to access the AppState service that I just registered in the DI container up above.

What is the most elegant way of accessing the AppState service instance?

I would prefer to not call services.BuildServiceProvider() inside the ConfigureServices method if at all possible.

services.AddSingleton<AppState>();

services.Configure<OpenIdConnectOptions>(AzureADB2CDefaults.OpenIdScheme, options =>
{
    options.Events = new OpenIdConnectEvents
    {
        OnTokenValidated = async ctx =>
        {
            //How to get access to instance of AppState, 
            //which was added to DI container up above
            AppState appState = //{get from DI somehow}; 
            appState.DoSomething();
        }
    };
});

EDIT: Using the answer below, I edited the code like so, but I can confirm that the OnTokenValidated event is not firing, as opposed to the code above in my original question, which does fire:

services.AddOptions<OpenIdConnectOptions>(AzureADB2CDefaults.OpenIdScheme)
            .Configure<IServiceScopeFactory>((options, sp) => {
                using (var scope = sp.CreateScope())
                {
                    options.Events = new OpenIdConnectEvents
                    {
                        OnTokenValidated = async ctx =>
                        {
                            var appState = scope.ServiceProvider.GetRequiredService<AppState>();

                            await appState.Dosomething();         
                        }
                    };
                }
            });

Answer 1

Use the TokenValidatedContext to get access to the current request service provider and resolve the service

services
    .Configure<OpenIdConnectOptions>(AzureADB2CDefaults.OpenIdScheme, options => {
        options.Events = new OpenIdConnectEvents {
            OnTokenValidated = async ctx => {
                //Get access to instance of AppState, 
                //which was added to DI container up above
                AppState appState = ctx.HttpContext.RequestServices
                    .GetRequiredService<AppState>();
                await appState.DoSomething();

                //...
            }
        };
    });