How to access User.Identity in BaseController

Question

When accessing the current user in my Windows authenticated .net core mvc app, User.Identity.Name returns Domain\Username. I am trying to implement a custom base controller so that I can change the User.Identity.Name to just Username and save it to a field for every controller that extends my base controller. I created an abstract class BaseController but when I try to access User.Identity.Name I get a null reference exception. I also tried Dependency Injection to use the HttpContextAccessor but then every controller that extends my BaseController gets an error. Here are the examples of what I tried:

public abstract class BaseController : Controller
{
    public readonly username;

    public BaseController()
    {
        username = User.Identity.Name.Split("\\")[1]; // Null reference exception
    }
}


public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpContextAccessor();
}

public abstract class BaseController : Controller
{
    public readonly username;

    public BaseController(IHttpContextAccessor httpContextAccessor)
    {
        username =httpContextAccessor.HttpContext.User.Identity.Name.Split("\\")[1];
    }
}

public HomeController : BaseController // Won't compile
{
    public IActionResult Index() 
    {
        ViewData["CurrentUser"] = username;
        return View();
    }
}

How can I do this?

Answer 1

The user principal is not available in any controller constructor. Create an extension method if all you want to do is split by "\".

public static class ExtensionMethods  
{  
    public static string GetUsername(this ClaimsPrincipal User)  
    {  
        return User.Identity.Name.Split("\\")[1];  
    }  
}  

Implementation is below but the code must be within an action.

User.GetUsername()  
  

Reference documentation
Extension Methods (C# Programming Guide)

Answer 2

also there is no good reason to inject an HttpContextAccessor into a controller. there is a performance hit, you use the controller property .HttpContext

just add a UserName property to the base controller:

public abstract class BaseController : Controller
{
       protected string? Username => User?.Identity?.Name?.Split("\\");
}