public class GitHubService
{
    public HttpClient Client { get; }

    public GitHubService(HttpClient client, HttpClientSettings httpClientSettings)
    {
        client.BaseAddress = new Uri("https://api.github.com/");
        client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); // GitHub API versioning
        client.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-Sample"); // GitHub requires a user-agent
        client.DefaultRequestHeaders.Add("Authorization", $"Bearer {httpClientSettings.BearerToken}");

        Client = client;
    }
}

// The typed client is registered as transient with DI.
services.AddHttpClient<GitHubService>();

services.AddSingleton<HttpClientSettings>();

public class HttpClientSettings
{
    public string BearerToken { get; set; }
}

var response = await _gitHubService.GetAsync("/repos/aspnet/docs/issues");