Dependency injection inside a FilterAttribute in ASP.NET MVC 6 - asp.net

Question

I'm struggling with ASP.NET MVC 6 (beta 4 release) trying to inject a service within a controller filter attribute of type AuthorizationFilterAttribute.
This is the service (it has another service injected)
public class UsersTableRepository
{
private readonly NeurosgarContext _dbContext;
public UsersTableRepository(NeurosgarContext DbContext)
{
_dbContext = DbContext;
}
public ICollection<User> AllUsers
{
get
{
return _dbContext.Users.ToList();
}
}
//other stuff...
}
This is the ConfigureServices method in Startup class for services enabling
public void ConfigureServices(IServiceCollection services)
{
//...
services.AddSingleton<NeurosgarContext>(a => NeurosgarContextFactory.GetContext());
services.AddSingleton<UifTableRepository<Nazione>>();
services.AddSingleton<UsersTableRepository>();
}
A simple "dummy" controller with two filters defined on it. You can notice that I already done DI inside this controller by decorating the property with [FromServices]and it works.
[Route("[controller]")]
[BasicAuthenticationFilter(Order = 0)]
[BasicAuthorizationFilter("Admin", Order = 1)]
public class DummyController : Controller
{
[FromServices]
public UsersTableRepository UsersRepository { get; set; }
// GET: /<controller>/
[Route("[action]")]
public IActionResult Index()
{
return View();
}
}
Doing the same DI within BasicAuthenticationFilterdoes not work and at runtime UserRepository property is a null reference.
public class BasicAuthenticationFilterAttribute : AuthorizationFilterAttribute
{
[FromServices]
public UsersTableRepository UsersRepository { get; set; }
public override void OnAuthorization(AuthorizationContext filterContext)
{
if (!Authenticate(filterContext.HttpContext))
{
// 401 Response
var result = new HttpUnauthorizedResult();
// Add the header for Basic authentication require
filterContext.HttpContext.Response.Headers.Append("WWW-Authenticate", "Basic");
filterContext.Result = result;
//if (!HasAllowAnonymous(context))
//{
// base.Fail(context);
//}
}
}
// ...
}
Any idea about how solve this?

Answer 1

Refrain from injecting dependencies into your attributes as explained here. Make your attributes passive, or make your attribute a humble object as described here.

Answer 2

var dependencyScope = context.HttpContext.RequestServices;
var usersRepository = dependencyScope.GetService(typeof(UsersTableRepository)) as UsersTableRepository;
// usersRepository is now ready to be used
So your BasicAuthenticationFilter will look like this:
public class BasicAuthenticationFilterAttribute : AuthorizationFilterAttribute
{
public UsersTableRepository UsersRepository { get; set; }
public override void OnAuthorization(AuthorizationContext filterContext)
{
var dependencyScope = context.HttpContext.RequestServices;
UsersRepository = dependencyScope.GetService(typeof(UsersTableRepository)) as UsersTableRepository;
if (!Authenticate(filterContext.HttpContext))
{
// 401 Response
var result = new HttpUnauthorizedResult();
// Add the header for Basic authentication require
filterContext.HttpContext.Response.Headers.Append("WWW-Authenticate", "Basic");
filterContext.Result = result;
//if (!HasAllowAnonymous(context))
//{
// base.Fail(context);
//}
}
}
// ...
}