OnyixSkins is a straightforward identity manager for Paper/Spigot servers.

It does exactly what it says:

/skin [Username]: Instantly change your look to match anyone else’s skin. /skins: Opens a clean menu where you can click on common/trending skins to apply them. /skin reset: Goes back to your original Mojang account skin.

All processing is done off the main thread so it won't lag your server. It’s "plug-and-play" with a minimal config file.