How to automatically refresh access token

I have an api with the following scopes (api_access and offline_access):

And a front end blazor app that uses code flow and consumes that api. Here's how I'm configuring authentication:

builder.Services.AddAuthentication(options =>            {                options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;                options.DefaultChallengeScheme = OpenIdConnectDefaults.AuthenticationScheme;            })            .AddCookie(CookieAuthenticationDefaults.AuthenticationScheme)            .AddOpenIdConnect(OpenIdConnectDefaults.AuthenticationScheme, options =>            {                options.SignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;                options.Authority = "xxxxx";                options.ClientId = "xxxxx";                options.ResponseType = "code";                options.SaveTokens = true;             options.Scope.Add("api://xxxxx/api_access");               options.ClientSecret = "xxxxx";

And here's how I'm requesting the access code to call the api:

var access_token = await httpContext.GetTokenAsync("access_token");

This works, but the access token expires in one hour. I don't get a new token when I call httpContext.GetTokenAsync("access_token") again after it is expired. How to get a new valid token?