C#: What is the IHttpClientFactory?

1// Program.cs
2builder.Services.AddHttpClient<IUserService, UserService>(client =>
3{
4    client.BaseAddress = new Uri("https://api.example.com");
5    client.DefaultRequestHeaders.Add("Accept", "application/json");
6});

1public class UserService
2{
3    private readonly HttpClient _client;
4
5    public UserService(HttpClient client)
6    {
7        _client = client;
8    }
9
10    public async Task<User> GetUserAsync(int id)
11    {
12        return await _client.GetFromJsonAsync<User>($"/users/{id}");
13    }
14}

1builder.Services.AddHttpClient<IUserService, UserService>()
2    .AddPolicyHandler(Policy
3        .Handle<HttpRequestException>()
4        .WaitAndRetryAsync(3, retryAttempt =>
5            TimeSpan.FromSeconds(Math.Pow(2, retryAttempt))));