Umbraco-CMS/src/Umbraco.Infrastructure/Security/BackOfficeUserValidator.cs

using Microsoft.AspNetCore.Identity;

namespace Umbraco.Cms.Core.Security;

public class BackOfficeUserValidator<T> : UserValidator<T>
    where T : BackOfficeIdentityUser
{
    public override async Task<IdentityResult> ValidateAsync(UserManager<T> manager, T user)
    {
        // Don't validate if the user's email or username hasn't changed otherwise it's just wasting SQL queries.
        if (user.IsPropertyDirty("Email") || user.IsPropertyDirty("UserName"))
        {
            return await base.ValidateAsync(manager, user);
        }

        return IdentityResult.Success;
    }
}