txAdmin has a built in whitelist feature which can be found in Settings → Player Manager. To add people from the whitelist first have the join the server then on the Players page their name will pop up in the Last 15 Whitelist Requests section. Just press accept. To remove on the same page you will see your previous actions, just click revoke on the whitelists you wish to remove.
If you’re community does have a discord server , then i would definetly suggest you to go with DiscordWhitelist System because when compared to TxAdmin’s Whitelist , It’s a nightmare for so many to just go to the panel and accept the players frequently , Tho if you are using a DiscordWhitelist system then you just need to put a whitelisted role into the Discord account of the player who is going to join the server, that itself can protect you’re server easily