Umbraco-CMS/src/Umbraco.Web.Common/Extensions/UmbracoApplicationBuilder.Identity.cs

using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.Security;

namespace Umbraco.Extensions
{
    public static partial class UmbracoApplicationBuilderExtensions
    {
        public static IUmbracoBuilder SetBackOfficeUserManager<TUserManager>(this IUmbracoBuilder builder)
            where TUserManager : UserManager<BackOfficeIdentityUser>, IBackOfficeUserManager
        {

            var customType = typeof(TUserManager);
            var userManagerType = typeof(UserManager<BackOfficeIdentityUser>);
            builder.Services.Replace(ServiceDescriptor.Scoped(typeof(IBackOfficeUserManager),customType));
            builder.Services.AddScoped(customType, services => services.GetRequiredService(userManagerType));
            builder.Services.Replace(ServiceDescriptor.Scoped(userManagerType,customType));
            return builder;
        }
    }
}