MudBlazorApp/TestApp02/Data/BiudAuthService.cs

using Microsoft.AspNetCore.Authentication.Cookies;
using System.Security.Claims;

namespace TestApp02.Data
{
    public class BiudAuthService
    {
        public BiudAuthService() {
            Users = new Dictionary<string, ClaimsPrincipal> ();
        }
        public Dictionary<string, ClaimsPrincipal> Users { get; set; }

        public ClaimsPrincipal AuthenticateUser(string p_LoginUser, string p_PasswordUser)
        {
            
            //ClaimsIdentity _ClaimsIdentity = new ClaimsIdentity();
            
            List<Claim>  _Claims = new List<Claim>{
                new Claim(ClaimTypes.Name, p_LoginUser),
                new Claim("Surname", "Surname"),
                new Claim ("Firstname", "Firstname"),
                new Claim ("Middlename", "Middlename"),
                new Claim ("Raion", "raion")
                };
            ClaimsIdentity _ClaimsIdentity = new ClaimsIdentity(_Claims, CookieAuthenticationDefaults.AuthenticationScheme);
            ClaimsPrincipal claimsPrincipal = new ClaimsPrincipal(_ClaimsIdentity);
            return claimsPrincipal;
        }
    }
}