User authentication flow with EOS + Steam

Development Programming & Scripting
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Hello Devs! My game is available on Steam and Epic Store and now I want to add user accounts (only Steam and EGS, I don’t want to force user to create new accounts). To store data I use backend server with Nakama.

Could you describe how should the user authentication flow look like?
What I have now:

Let user login:

FOnlineAccountCredentials OnlineAccountCredentials;
OnlineAccountCredentials.Type = "accountportal";
OnlineAccountCredentials.Id = "";
OnlineAccountCredentials.Token = "";
IdentityInterfacePtr->Login(0, OnlineAccountCredentials);

Then I have a delegate on login completed and I can get user AccessToken:

void UEOSHandleSubsystem::LoginCompleted(int numOfPlayers, bool bWasSuccessful, const FUniqueNetId& UserId, const FString& Error)
{
	if(!IdentityInterfacePtr)
	{return;}

	TSharedPtr<FUserOnlineAccount> UserOnlineAccount = IdentityInterfacePtr->GetUserAccount(UserId);
	FString AccessToken = UserOnlineAccount->GetAccessToken();
	OnEOSLoginCompleted.Broadcast(bWasSuccessful, Error, AccessToken);
}

I can store the token in the backend Api, but how can I use this token so the user doesn’t need to login every time?

Thank you very much for all your answers!