Access the current HttpContext in ASP.NET Core

Secret tip for those migrating large chunks of code.

The following method is an evil carbuncle of a hack which is actively engaged in carrying out the express work of Satan (in the eyes of .NET Core framework developers), but it works:

In public class Startup

add a property

public IConfigurationRoot Configuration { get; }

And then add a singleton IHttpContextAccessor to DI in ConfigureServices.

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<Microsoft.AspNetCore.Http.IHttpContextAccessor, Microsoft.AspNetCore.Http.HttpContextAccessor>();

Then in Configure

    public void Configure(
              IApplicationBuilder app
             ,IHostingEnvironment env
             ,ILoggerFactory loggerFactory
    )
    {

add the DI Parameter IServiceProvider svp, so the method looks like:

    public void Configure(
           IApplicationBuilder app
          ,IHostingEnvironment env
          ,ILoggerFactory loggerFactory
          ,IServiceProvider svp)
    {

Next, create a replacement class for System.Web:

namespace System.Web
{

    namespace Hosting
    {
        public static class HostingEnvironment 
        {
            public static bool m_IsHosted;

            static HostingEnvironment()
            {
                m_IsHosted = false;
            }

            public static bool IsHosted
            {
                get
                {
                    return m_IsHosted;
                }
            }
        }
    }


    public static class HttpContext
    {
        public static IServiceProvider ServiceProvider;

        static HttpContext()
        { }


        public static Microsoft.AspNetCore.Http.HttpContext Current
        {
            get
            {
                // var factory2 = ServiceProvider.GetService<Microsoft.AspNetCore.Http.IHttpContextAccessor>();
                object factory = ServiceProvider.GetService(typeof(Microsoft.AspNetCore.Http.IHttpContextAccessor));

                // Microsoft.AspNetCore.Http.HttpContextAccessor fac =(Microsoft.AspNetCore.Http.HttpContextAccessor)factory;
                Microsoft.AspNetCore.Http.HttpContext context = ((Microsoft.AspNetCore.Http.HttpContextAccessor)factory).HttpContext;
                // context.Response.WriteAsync("Test");

                return context;
            }
        }


    } // End Class HttpContext 


}

Now in Configure, where you added the IServiceProvider svp, save this service provider into the static variable "ServiceProvider" in the just created dummy class System.Web.HttpContext (System.Web.HttpContext.ServiceProvider)

and set HostingEnvironment.IsHosted to true

System.Web.Hosting.HostingEnvironment.m_IsHosted = true;

this is essentially what System.Web did, just that you never saw it (I guess the variable was declared as internal instead of public).

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IServiceProvider svp)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();

    ServiceProvider = svp;
    System.Web.HttpContext.ServiceProvider = svp;
    System.Web.Hosting.HostingEnvironment.m_IsHosted = true;
    

    app.UseCookieAuthentication(new CookieAuthenticationOptions()
    {
        AuthenticationScheme = "MyCookieMiddlewareInstance",
        LoginPath = new Microsoft.AspNetCore.Http.PathString("/Account/Unauthorized/"),
        AccessDeniedPath = new Microsoft.AspNetCore.Http.PathString("/Account/Forbidden/"),
        AutomaticAuthenticate = true,
        AutomaticChallenge = true,
        CookieSecure = Microsoft.AspNetCore.Http.CookieSecurePolicy.SameAsRequest

       , CookieHttpOnly=false
     
    });

Like in ASP.NET Web-Forms, you'll get a NullReference when you're trying to access a HttpContext when there is none, such as it used to be in Application_Start in global.asax.

I stress again, this only works if you actually added

services.AddSingleton<Microsoft.AspNetCore.Http.IHttpContextAccessor, Microsoft.AspNetCore.Http.HttpContextAccessor>();

like I wrote you should.
Welcome to the ServiceLocator pattern within the DI pattern ;)
For risks and side effects, ask your resident doctor or pharmacist - or study the sources of .NET Core at github.com/aspnet, and do some testing.

Perhaps a more maintainable method would be adding this helper class

namespace System.Web
{

    public static class HttpContext
    {
        private static Microsoft.AspNetCore.Http.IHttpContextAccessor m_httpContextAccessor;


        public static void Configure(Microsoft.AspNetCore.Http.IHttpContextAccessor httpContextAccessor)
        {
            m_httpContextAccessor = httpContextAccessor;
        }


        public static Microsoft.AspNetCore.Http.HttpContext Current
        {
            get
            {
                return m_httpContextAccessor.HttpContext;
            }
        }


    }


}

And then calling HttpContext.Configure in Startup->Configure

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IServiceProvider svp)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();


    System.Web.HttpContext.Configure(app.ApplicationServices.
        GetRequiredService<Microsoft.AspNetCore.Http.IHttpContextAccessor>()
    );

The most legit way I came up with was by injecting IHttpContextAccessor in your static implementation as follow:

public static class HttpHelper
{
     private static IHttpContextAccessor _accessor;
     public static void Configure(IHttpContextAccessor httpContextAccessor)
     {
          _accessor = httpContextAccessor;
     }

     public static HttpContext HttpContext => _accessor.HttpContext;
}

Then assigning the IHttpContextAccessor in the Startup Configure should do the job.

HttpHelper.Configure(app.ApplicationServices.GetRequiredService<IHttpContextAccessor>());

I guess you should also need to register the service singleton:

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

Just to add to the other answers...

In ASP.NET Core 2.1, there's the AddHttpContextAccessor extension method, that will register the IHttpContextAccessor with the correct lifetime:

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddHttpContextAccessor();

        // Other code...
    }
}

According to this article: Accessing HttpContext outside of framework components in ASP.NET Core

namespace System.Web
{
    public static class HttpContext
    {
        private static IHttpContextAccessor _contextAccessor;

        public static Microsoft.AspNetCore.Http.HttpContext Current => _contextAccessor.HttpContext;

        internal static void Configure(IHttpContextAccessor contextAccessor)
        {
            _contextAccessor = contextAccessor;
        }
    }
}

Then:

public static class StaticHttpContextExtensions
{
    public static void AddHttpContextAccessor(this IServiceCollection services)
    {
        services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
    }

    public static IApplicationBuilder UseStaticHttpContext(this IApplicationBuilder app)
    {
        var httpContextAccessor = app.ApplicationServices.GetRequiredService<IHttpContextAccessor>();
        System.Web.HttpContext.Configure(httpContextAccessor);
        return app;
    }
}

Then:

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

    public void Configure(IApplicationBuilder app)
    {
        app.UseStaticHttpContext();
        app.UseMvc();
    }
}

You can use it like this:

using System.Web;

public class MyService
{
   public void DoWork()
   {
    var context = HttpContext.Current;
    // continue with context instance
   }
}

In Startup

services.AddHttpContextAccessor();

In Controller

public class HomeController : Controller
    {
        private readonly IHttpContextAccessor _context;

        public HomeController(IHttpContextAccessor context)
        {
            _context = context; 
        }
        public IActionResult Index()
        {
           var context = _context.HttpContext.Request.Headers.ToList();
           return View();
        }
   }

To access to the session object from a class without explicitly use dependency injection in class constructor follow the next steps:

1. Add a Singleton instance on Startup.cs (ConfigureServices):

   services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
   

2. In your target class declare an instance of HttpContextAccessor:

   IHttpContextAccessor _httpContextAccessor = new HttpContextAccessor();
   

3. Access to the session object :

   string mySessionVar = _httpContextAccessor.HttpContext.Session.GetString("_MySessionVar");
   

EXAMPLE

Startup.cs

public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

    }

YourClass.cs

public class YourClass {
      
       public string yourProperty {
             get{
                 IHttpContextAccessor _httpContextAccessor = new HttpContextAccessor();
                 return _httpContextAccessor.HttpContext.Session.GetString("_YourSessionVar");         
                }
        }
  }

Enjoy :)