Umbraco-CMS/src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs

using System;
using System.Security.Claims;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features;
using Umbraco.Cms.Core.Security;

namespace Umbraco.Extensions
{
    public static class HttpContextExtensions
    {
        public static void SetPrincipalForRequest(this HttpContext context, ClaimsPrincipal principal)
        {
            context.User = principal;
        }


        public static void SetReasonPhrase(this HttpContext httpContext, string reasonPhrase)
        {
            //TODO we should update this behavior, as HTTP2 do not have ReasonPhrase. Could as well be returned in body
            // https://github.com/aspnet/HttpAbstractions/issues/395
            var httpResponseFeature = httpContext.Features.Get<IHttpResponseFeature>();
            if (!(httpResponseFeature is null))
            {
                httpResponseFeature.ReasonPhrase = reasonPhrase;
            }
        }

        /// <summary>
        /// This will return the current back office identity.
        /// </summary>
        /// <param name="http"></param>
        /// <returns>
        /// Returns the current back office identity if an admin is authenticated otherwise null
        /// </returns>
        public static ClaimsIdentity GetCurrentIdentity(this HttpContext http)
        {
            if (http == null) throw new ArgumentNullException(nameof(http));
            if (http.User == null) return null; //there's no user at all so no identity

            // If it's already a UmbracoBackOfficeIdentity
            var backOfficeIdentity = http.User.GetUmbracoIdentity();
            if (backOfficeIdentity != null) return backOfficeIdentity;

            return null;
        }
    }
}