MCAP is a plugin for improving vanilla whitelist and it provides integration with Discord if you want to get fancy whitelist requests on your Discord server without hard setup.

How to use whitelist (config):
Make sure you have Minecraft's whitelist disabled (if not, use /whitelist off or set white-list=false in server.properties)
Add players you need in whitelist: players:
Set whitelist: enabled: true

How to use whitelist:
Make sure you have Minecraft's whitelist disabled (if not, use /whitelist off)
Add players you need using /mcapwl add [nickname] (make sure to add yourself)
Enter /mcapwl on. Now non-whitelisted players can't join your server!

Also, you can change kick message in config:
messages: notinwhitelist: "any text you want when player is kicked"

Commands:
Whitelist:
/mcapwl - Permission: mcap.admin.whitelist
/mcapwl on/off - Disable or enable whitelist
/mcapwl list - Get all players in whitelist
/mcapwl add [nickname] - Add player to whitelist
/mcapwl bulkadd [nicknames separated by commas] - Add players to whitelist - Example: /mcapwl bulkadd princetrouble,stopper,stopper_
/mcapwl remove [nickname] - Remove player from whitelist
/mcapwl bulkremove [nicknames separated by commas] - Remove players from whitelist - Example: /mcapwl bulkremove princetrouble,stopper,stopper_
/mcapwl reload - Reloads config
Discord integration:
/mcapdisetup - Use this command to get Discord integration setup instructions - Permission: mcap.admin.mcapconfig
/mcaptoken [token] - Set MCAP Token - Permission: mcap.admin.mcapconfig
/mcapinvite [Discord Invite List] - Set invite link that will be shown when you use /invite - Permission: mcap.admin.mcapconfig
/mcapdisable - Toggles Discord whitelist integration (do not enable if you don't have token), off by default - Permission: mcap.admin.mcapconfig
/invite - Show invite to your Discord (set link using /mcapinvite)

Permissions:
mcap.*
mcap.player.* # unused
mcap.admin.*
mcap.admin.mcapconfig - Allows usage of /mcapdisetup, /mcaptoken, /mcapinvite
mcap.admin.disable - Allows usage of /mcapdisable
mcap.admin.whitelist - Allows usage of /mcapwl

How to use Discord integration:
Firstly, you need to have a Discord Server.
Invite a bot from website https://mcauth.one/en and in Server Settings on MCAuth.one, open tab "Channels for requests" and click "Enter channels for requests management.".
Where it says "Select channel for request", select your, well, channel for requests. Type in IP, check "Enable MCAP checkbox" and press "Create settings for channel".
Copy token from above created channel configuration and run command on your Minecraft server: /mcaptoken [token you just copied] (or set token in config.yml)
Open config.yml and change polldisabled to false
In your Discord server, change language using /lang en or change language in MCAuth Server Settings.
Now, users of your Discord server can use /req command to send fancy request. You can click Accept in request and player will be whitelisted! (assuming you did all steps correct)

This plugin uses bStats: https://bstats.org/plugin/bukkit/MCAP/14538