AspNetCore.Docs/aspnetcore/migration/claimsprincipal-current.md

title	author	description	ms.author	ms.custom	ms.date	uid
Migrate from ClaimsPrincipal.Current	mjrousos	Learn how to migrate away from ClaimsPrincipal.Current to retrieve the current authenticated user's identity and claims in ASP.NET Core.	scaddie	mvc	03/26/2019	migration/claimsprincipal-current

Migrate from ClaimsPrincipal.Current

In ASP.NET 4.x projects, it was common to use ClaimsPrincipal.Current to retrieve the current authenticated user's identity and claims. In ASP.NET Core, this property is no longer set. Code that was depending on it needs to be updated to get the current authenticated user's identity through a different means.

Context-specific data instead of static data

When using ASP.NET Core, the values of both ClaimsPrincipal.Current and Thread.CurrentPrincipal aren't set. These properties both represent static state, which ASP.NET Core generally avoids. Instead, ASP.NET Core's architecture is to retrieve dependencies (like the current user's identity) from context-specific service collections (using its dependency injection (DI) model). What's more, Thread.CurrentPrincipal is thread static, so it may not persist changes in some asynchronous scenarios (and ClaimsPrincipal.Current just calls Thread.CurrentPrincipal by default).

To understand the sorts of problems thread static members can lead to in asynchronous scenarios, consider the following code snippet:

// Create a ClaimsPrincipal and set Thread.CurrentPrincipal
var identity = new ClaimsIdentity();
identity.AddClaim(new Claim(ClaimTypes.Name, "User1"));
Thread.CurrentPrincipal = new ClaimsPrincipal(identity);

// Check the current user
Console.WriteLine($"Current user: {Thread.CurrentPrincipal?.Identity.Name}");

// For the method to complete asynchronously
await Task.Yield();

// Check the current user after
Console.WriteLine($"Current user: {Thread.CurrentPrincipal?.Identity.Name}");

The preceding sample code sets Thread.CurrentPrincipal and checks its value before and after awaiting an asynchronous call. Thread.CurrentPrincipal is specific to the thread on which it's set, and the method is likely to resume execution on a different thread after the await. Consequently, Thread.CurrentPrincipal is present when it's first checked but is null after the call to await Task.Yield().

Getting the current user's identity from the app's DI service collection is more testable, too, since test identities can be easily injected.

Retrieve the current user in an ASP.NET Core app

There are several options for retrieving the current authenticated user's ClaimsPrincipal in ASP.NET Core in place of ClaimsPrincipal.Current:

• ControllerBase.User. MVC controllers can access the current authenticated user with their User property.

• HttpContext.User. Components with access to the current HttpContext (middleware, for example) can get the current user's ClaimsPrincipal from HttpContext.User.

• Passed in from caller. Libraries without access to the current HttpContext are often called from controllers or middleware components and can have the current user's identity passed as an argument.

• IHttpContextAccessor. The project being migrated to ASP.NET Core may be too large to easily pass the current user's identity to all necessary locations. In such cases, IHttpContextAccessor can be used as a workaround. IHttpContextAccessor is able to access the current HttpContext (if one exists). If DI is being used, see xref:fundamentals/httpcontext. A short-term solution to getting the current user's identity in code that hasn't yet been updated to work with ASP.NET Core's DI-driven architecture would be:

  • Make IHttpContextAccessor available in the DI container by calling AddHttpContextAccessor in Startup.ConfigureServices.
  • Get an instance of IHttpContextAccessor during startup and store it in a static variable. The instance is made available to code that was previously retrieving the current user from a static property.
  • Retrieve the current user's ClaimsPrincipal using HttpContextAccessor.HttpContext?.User. If this code is used outside of the context of an HTTP request, the HttpContext is null.

The final option, using an IHttpContextAccessor instance stored in a static variable, is contrary to ASP.NET Core principles (preferring injected dependencies to static dependencies). Plan to eventually retrieve IHttpContextAccessor instances from dependency injection instead. A static helper can be a useful bridge, though, when migrating large existing ASP.NET apps that were previously using ClaimsPrincipal.Current.