Setup HttpClient configuration in Startup.ConfigureService

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
    
    //configure httpclient service
    services.AddHttpClient("GithubAPI", client=> 
    {
        //customize as per your need
        client.BaseAddress = new Uri("http://api.github.com/");
        client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json");
        client.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactoryExample");
    }); 
}