adding hidden basic asp.net core backend (#30)

Base functionality:

    DB
    email sending
    user registration & login
    storing new characters and reading them back

Notes:

    Functionality is "hidden" with no links pointing to it.
    Most pages are scaffolded and not reviewed at all :(
    local Dev db setup is pushed to git
    NO local email setup :(

Kemkas.Web/Services/Identity/ICurrentUserService.cs

@@ -0,0 +1,41 @@
+using Kemkas.Web.Db.Models;
+using Microsoft.AspNetCore.Identity;
+
+namespace Kemkas.Web.Services.Identity;
+
+public interface ICurrentUserService
+{
+    public Task<ApplicationUser?> GetCurrentUser();
+
+    public Task<ApplicationUser> GetCurrentUserOrThrow();
+}
+
+public class CurrentUserService(
+    IHttpContextAccessor httpContextAccessor,
+    UserManager<ApplicationUser> userManager
+    ) : ICurrentUserService
+{
+    private ApplicationUser? _user;
+    
+    public async Task<ApplicationUser?> GetCurrentUser()
+    {
+        if (_user is not null)
+        {
+            return _user;
+        }
+
+        var userName = httpContextAccessor.HttpContext?.User.Identity?.Name;
+        if (userName is null)
+        {
+            return null;
+        }
+
+        _user = await userManager.FindByNameAsync(userName);
+        return _user;
+    }
+
+    public async Task<ApplicationUser> GetCurrentUserOrThrow()
+    {
+        return await GetCurrentUser() ?? throw new InvalidOperationException("no current user!");
+    }
+}