in app/Data/AppUserStore.cs [112:120]
public Task SetNormalizedUserNameAsync(AppUser user, string normalizedName, CancellationToken cancellationToken)
{
cancellationToken.ThrowIfCancellationRequested();
if (user == null) throw new ArgumentNullException(nameof(user));
if (normalizedName == null) throw new ArgumentNullException(nameof(normalizedName));
user.NormalizedUserName = normalizedName;
return Task.FromResult<object>(null);
}