How to get the authenticated user from a separate class library in .Net Core

Question

I have an MVC core app that references a .NET Core class library. All of the data access and business logic is in the class library. How can I can I access the authenticated user from the class library?

In the past using .NET Framework you could use

string UserName = System.Web.HttpContext.Current.User.Identity.Name

To get the username from inside a method in the class library. In .NET Core, it appears that HttpContext no longer has a Current or User property.

Here's a simple use case. Suppose I have a data entity and service that "stamps" entities with the date and username before saving them to the database.

These would be in the external class library:

public interface IAuditable{
    DateTime CreateDate{get;set;}
    string UserName{get;set;}
}

public class MyEntity:IAuditable{
    public int ID{get;set;}
    public string Name{get;set;}
    public string Information{get;set;}
}

public static class Auditor{
    public static IAuditable Stamp(IAuditable model){            
        model.CreateDate=DateTime.UtcNow;
        model.CreatedBy=System.Web.HttpContext.Current.User.Identity.Name;
        return model;
    }
}

public sealed class MyService:IDisposable{
    MyDb db=new MyDb();
    public async Task<int> Create(MyEntity model){
        Auditor.Stamp(model);
        db.MyEntities.Add(model);
        return await db.SaveAsync();
    }
    public void Dispose(){
        db.Dispose();
    }
}

Then in my MVC controller I'd have a post action that calls the service:

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create(MyEntity model)
{
    await service.Create(model);
    return RedirectToAction("Index")
}

I would like a way to replace that line in Auditor.Stamp since there's no HttpContext.Current in .NET Core, apparently.

This post gives an example of how to get the username in Core:

public class UserResolverService  
{
    private readonly IHttpContextAccessor _context;
    public UserResolverService(IHttpContextAccessor context)
    {
        _context = context;
    }

    public string GetUser()
    {
       return await _context.HttpContext.User?.Identity?.Name;
    }
}

But I'm left with another version of the same problem: how do I get a IHttpContextAccessor object from inside the class library?

Most of my search results only deal with the question of how to get the User name from inside an MVC controller method. In the past I've passed a User object into every method for every service but that's a lot of extra typing--I'd rather have something I can type once (maybe inside Startup?) And then forget about it.

I do want something I can mock for unit tests, but honestly I think wrapping System.Web.HttpContext.Current.User.Identity.Name in something that can be mocked was pretty darn easy.

just inject the IHttpContextAccessor and you have access to what you need. — Nkosi

Nkosi Nkosi · Accepted Answer · 2018-05-24T15:31:35

The same flexibility still exists in this version.

Inject the IHttpContextAccessor and you have access to what you need.

refactor the static Auditor to be more injectable

public interface IAuditor {
    IAuditable Stamp(IAuditable model);
}

public class Auditor : IAuditor {
    private readonly IHttpContextAccessor accessor;

    public Auditor(IHttpContextAccessor accessor) {
        this.accessor = accessor;
    }

    public IAuditable Stamp(IAuditable model){            
        model.CreateDate = DateTime.UtcNow;
        model.CreatedBy = accessor.HttpContext.User?.Identity?.Name;
        return model;
    }
}

The service would then depend on the new abstraction

public interface IMyService : IDisposable {
    Task<int> Create(MyEntity model);
}

public sealed class MyService : IMyService {
    MyDb db = new MyDb();
    private readonly IAuditor auditor;

    public MyService(IAuditor auditor) {
        this.auditor = auditor;
    }

    public async Task<int> Create(MyEntity model) {
        auditor.Stamp(model);
        db.MyEntities.Add(model);
        return await db.SaveAsync();
    }

    public void Dispose() {
        db.Dispose();
    }
}

You should really also be injecting the MyDb as well but that is outside of the scope of the current question.

Lastly you configure you library to be able to setup the services during start up

public static IServiceCollection AddMyLibrary(this IServiceCollection services) {

    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
    services.AddSingleton<IAuditor, Auditor>();  
    services.AddScoped<IMyService, MyService>();

    //...add other services as needed

    return services.  
}

and then you can call it in Start up from the root project

public void ConfigureServices(IServiceCollection services) {

    //...

    services.AddMyLibrary();

    //...
}

With these abstraction and using DI app parts are decoupled and can be tested in isolation.

How to get the authenticated user from a separate class library in .Net Core

1 Answers