[PrincipalPermissionAttribute(SecurityAction.Demand, Role = "MyRole")]

AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);

[HttpPost]
        [AllowAnonymous]
        [ValidateAntiForgeryToken]
        public ActionResult LogOn(User user, string returnUrl)
        {
            if (this.ModelState.IsValid)
            {
                if (_userService.IsValid(user))
                {
                    int userID = _userService.GetUser(u => u.Username == user.Username && u.Password == user.Password).Id;
                    FormsAuthentication.SetAuthCookie(userID.ToString(CultureInfo.InvariantCulture), user.RememberMe);
                    if (shouldRedirect(returnUrl))
                    {
                        return Redirect(returnUrl);
                    }
                    FormsAuthentication.RedirectFromLoginPage(userID.ToString(CultureInfo.InvariantCulture), user.RememberMe);
                }
            }
            this.ModelState.AddModelError("", "The user name or password provided is incorrect.");
            ViewBag.Error = "Login faild! Make sure you have entered the right user name and password!";
            return View(user);
        }

public interface IRoleService
    {
        bool IsUserInRole(string username, string roleName);
        string[] GetRolesForUser(string username);
        void AddUsersToRoles(string[] usernames, string[] roleNames);
        string ApplicationName { get; set; }
        void CreateRole(string roleName);
        bool DeleteRole(string roleName, bool throwOnPopulatedRole);
        string[] FindUsersInRole(string roleName, string usernameToMatch);
        string[] GetAllRoles();
        string[] GetUsersInRole(string roleName);
        void RemoveUsersFromRoles(string[] usernames, string[] roleNames);
        bool RoleExists(string roleName);
    }

public class RoleService: IRoleService
{
        private readonly IDbSet<Role> _role;
        private readonly IUnitOfWork _uow;
        public RoleService(IUnitOfWork uow)
        {
            _uow = uow;
            _role = uow.Set<Role>();
        }
        public bool IsUserInRole(string username, string roleName)
        {
            throw new NotImplementedException();
        }
        public string[] GetRolesForUser(string username)
        {
            throw new NotImplementedException();
        }
//...
}