API Token Renewal in ASP.NET 6.0

ExampleClient.cs

using System.Net.Http.Headers;

public interface IExampleClient
{
    /* interface methods here */
}

public class ExampleClient : IExampleClient
{
    public static string AccessToken { get; set; }

    private readonly HttpClient _client;

    public ExampleClient(HttpClient client)
    {
        _client = client;
        _client.BaseAddress = new Uri("https://api.example.com/");
        _client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", AccessToken);
    }

    /* implement interface */
}

Startup.cs

using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.DependencyInjection;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddHttpClient<IExampleClient, ExampleClient>();

        // if you want to change the token duration, do it before here
        // TokenRenewalService.TokenDurationSeconds = 15 * 60; // 15 minutes
        services.AddHttpClient<TokenRenewalService>();
        services.AddHostedService<TokenRenewalService>();
    }
}

TokenRenewalService.cs

using Microsoft.Extensions.Hosting;
using FluentHttpClient;

public class TokenRenewalService : BackgroundService, IDisposable
{
    public static int TokenDurationSeconds { get; set; } = 5 * 60; // 5 minutes

    private readonly HttpClient _client;
    private readonly FormUrlEncodedContent _content;

    public TokenRenewalService(HttpClient client)
    {
        _client = client;
        _client.BaseAddress = new Uri("https://api.example.com/");

        _content = new FormUrlEncodedContent(new Dictionary<string, string>
        {
            {"username", "my-username"},
            {"password", "my-password"}
        });
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        // Get the token right away!
        await RenewAccessToken();

        // Now set a timer for 10 seconds before our token expires.
        var timer = new PeriodicTimer(TimeSpan.FromSeconds(TokenDurationSeconds - 10));

        // And as long as our timer is running, we'll keep renewing the token!
        while (await timer.WaitForNextTickAsync(stoppingToken))
        {
            await RenewAccessToken();
        }
    }

    private async Task RenewAccessToken()
    {
        var response = await _client.UsingRoute("authenticate")
            .WithContent(_content)
            .PostAsync()
            .GetResponseStringAsync();

        ExampleClient.AccessToken = response;
    }

    public override void Dispose()
    {
        _client.Dispose();
        base.Dispose();
    }
}