Usage:

Put this class into /framework/rbac/MongoDbManager.php
And change config

$config = [
	...
	'components' => [
		...
		'mongodb' => [
			'class' => '\yii\mongodb\Connection',
			'dsn' => 'mongodb://localhost:27017/dbname',
		],
	
		'authManager' => [
			'class' => 'yii\rbac\MongoDbManager',
			'defaultRoles' => ['guest'],
		],
		...
	],
	...
];