Set up Discord login

Game Instance variable: DiscordLoginBusy (Boolean, false).

Game module dependencies: DiscordGame, BetideCore, Engine.

// DiscordLoginGameInstance.h
#pragma once

#include "Engine/GameInstance.h"
#include "DiscordLoginGameInstance.generated.h"

UCLASS()
class UDiscordLoginGameInstance : public UGameInstance
{
    GENERATED_BODY()
  public:
    UFUNCTION(BlueprintCallable)
    void SignInToDiscord();

  private:
    bool DiscordLoginBusy = false;
};

// DiscordLoginGameInstance.cpp
#include "DiscordLoginGameInstance.h"
#include "DiscordGameSubsystem.h"
#include "Nodes/Discord_GetAuthToken_AsyncFunction.h"

DEFINE_LOG_CATEGORY_STATIC(LogGameDiscordLogin, Log, All);

void UDiscordLoginGameInstance::SignInToDiscord()
{
    if (DiscordLoginBusy)
    {
        UE_LOG(LogGameDiscordLogin, Warning, TEXT("Discord sign-in is already running"));
        return;
    }
    DiscordLoginBusy = true;
    auto *Login = UDiscord_GetAuthToken_AsyncFunction::GetDiscordAuthToken(this);
    if (!Login)
    {
        DiscordLoginBusy = false;
        UE_LOG(LogGameDiscordLogin, Error, TEXT("Could not create Discord login action"));
        return;
    }
    const TWeakObjectPtr<UDiscordLoginGameInstance> WeakThis(this);
    Login->CompletionCallback = [WeakThis](const FString &, const FBetideError &Error) {
        UDiscordLoginGameInstance *Self = WeakThis.Get();
        if (!Self)
            return;
        Self->DiscordLoginBusy = false;
        if (Error.IsError())
        {
            UE_LOG(LogGameDiscordLogin, Warning, TEXT("%s"), *Error.Message);
            return;
        }
        if (const UDiscordGameSubsystem *Discord = Self->GetSubsystem<UDiscordGameSubsystem>())
        {
            UE_LOG(LogGameDiscordLogin, Log, TEXT("Discord ready: %s (%lld)"),
                   *Discord->GetDiscordDisplayName(), Discord->GetDiscordUserId());
        }
    };
    Login->Activate();
}