The UIUserProvider is used for creating user within limitting input information.

If you want to add more infomation freely while registering new user then you could use ApplicationUserManager<ApplicationUser> instead of using UIUserProvider

Can you provide simple sample of ApplicationUserManager<ApplicationUser>? The one in QuickSilver is complex and entangled with much code to begin with. I used the code below which gives me null.

 public ApplicationUserManager UserManager
        {
            get
            {
                return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
            }
            private set
            {
                _userManager = value;
            }
        }

Here is simple sample of  ApplicationUserManager<ApplicationUser> to create a new user

var userManager = ServiceLocator.Current.GetInstance<ApplicationUserManager<ApplicationUser>>();
userManager.Create(new ApplicationUser() {Username = "test", Email = "test@example.com", IsApproved = true}, "Password4Test");

When I used the code you provided, I am getting the following error.

No default Instance is registered and cannot be automatically determined for type 'IUserStore<ApplicationUser>'

There is no configuration specified for IUserStore<ApplicationUser>

1.) new ApplicationUserManager(*Default of IUserStore<ApplicationUser>*)
2.) ApplicationUserManager
3.) Instance of ApplicationUserManager
4.) Container.GetInstance(Login.ApplicationUserManager)

Exception Details: StructureMap.StructureMapConfigurationException: No default Instance is registered and cannot be automatically determined for type 'IUserStore<ApplicationUser>'

It is so weird. I did it successfully before based on this example https://github.com/episerver/QuicksilverB2B/blob/master/Sources/EPiServer.Reference.Commerce.Site/Features/Login/Services/UserService.cs

There may be a change for this stuff with new episerver version. I will try to find out the problem when I have time

Injecting last two dependencies provided me Usermanager object.

 context.Services.AddTransient<IContentRenderer, ErrorHandlingContentRenderer>()
                    .AddTransient<ContentAreaRenderer, AlloyContentAreaRenderer>()
                    .AddTransient<IUserStore<ApplicationUser>, UserStore<ApplicationUser>>()
                    .AddTransient<DbContext, ApplicationDbContext>();

Great! You are right. These were not registered automatically by Episerver.