OurWindowsPrincipalHandler.cs

public class OurWindowsPrincipalHandler : IWindowsPrincipalHandler
{
    private readonly ITransaction _transaction;

    public OurWindowsPrincipalHandler(ITransaction transaction)
    {
        _transaction = transaction;
    }
    
    public bool Authenticated(IPrincipal principal)
    {
        _transaction.WithRepository(repository =>
        {
            if (repository.All<User>().Any(x => x.UserName == principal.Identity.Name)) return;

            repository.Update(new User { UserName = principal.Identity.Name });
        });
        
        return true;
    }
}

ReplaceService.cs

ReplaceService<IWindowsPrincipalHandler, OurWindowsPrincipalHandler>();