The code you’ve made is incomplete as @user681574 stated, so unfortunately your question will be answered in a vague way.
It seems like you have to make objects appear when the player has successfully logged in as it is the easiest way possible. Another way is to make the players not able to register clicks/keys until they have logged in. In this way, the player will be “frozen” and forced to login. Also be sure to add a timeout to avoid having your server full of AFK players or bot-attacks.
Good luck with your plugin!
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solved Minecraft Login system