wiki.techinc.nl/includes/user/Hook/UserAddGroupHook.php

<?php

namespace MediaWiki\User\Hook;

use MediaWiki\User\User;

/**
 * This is a hook handler interface, see docs/Hooks.md.
 * Use the hook name "UserAddGroup" to register handlers implementing this interface.
 *
 * @stable to implement
 * @ingroup Hooks
 */
interface UserAddGroupHook {
	/**
	 * This hook is called when adding a group or changing a group's expiry.
	 *
	 * @since 1.35
	 *
	 * @param User $user The user that is to have a group added
	 * @param string &$group The group to add; can be modified
	 * @param string|null &$expiry The expiry time in TS_MW format, or null if the group is not to
	 *   expire; can be modified
	 * @return bool|void True or no return value to continue or false to abort (not add the group)
	 */
	public function onUserAddGroup( $user, &$group, &$expiry );
}