BungeeGuard is a plugin used to protect against BungeeCord's UUID spoof exploit which allows users to join without authenticating through the BungeeCord proxy, allowing them to join as any user.
Make sure your BungeeCord is on the latest version. Also, make sure to use version 1.2 or later of BungeeGuard as previous versions have an issue.
After you have restarted the servers you installed BungeeGuard on, enter the
config.yml file located in your BungeeCord's BungeeGuard directory and copy the authentication token. Paste this authentication token into the
config.yml file within your Spigot servers' BungeeGuard directory.
# Allowed authentication tokens. allowed-tokens: - "AUSXEwebkOGVnbihJM8gBS0QUutDzvIG009xoAfo1Huba9pGvhfjrA21r8dWVsa8"
Now, restart all your servers you installed BungeeGuard on and test to see if it's properly working!