GetAuthToken returns an empty string after login to the Game Center

Development Programming & Scripting Blueprint
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1

FString UMobileUtilsBlueprintLibrary::GetAuthToken()
{
auto OnlineSubsystem = IOnlineSubsystem::Get();
OnlineSubsystem->GetIdentityInterface()->GetAuthToken(0);
}

If i use the above function after login to Game Center, an empty string is returned.
Thank you in advance.