dependency-injection-based-on-request-headers.cs

public interface IMessageService
{
    string GetMessage();
}

[ApiController]
[Route("")]
public class MyController : ControllerBase
{
    private readonly IMessageService _messageService;

    public MyController(IMessageService messageService)
    {
        _messageService = messageService;
    }

    [HttpGet]
    public string Get()
    {
        return _messageService.GetMessage();
    }
}