public static function & GetInstance ($configuration = []) {
		if (self::$instance === NULL) {
			$authClass = self::GetAuthClass();
			self::$instance = & $authClass::GetInstance($configuration);
		}
		return self::$instance;
	}
public static function & GetInstance ($configuration = []) {
		if (self::$instance === NULL) {
			$authClass = self::GetAuthClass();
			self::$instance = & $authClass::GetInstance($configuration);
		}
		return self::$instance;
	}
Return singleton instance. If instance exists, return existing instance,
if not, create new authentication module instance by existing classes,
store it and return it. Try to create authentication modules in this order:
- `\MvcCore\Ext\Auths\Full` - if class exists
- `\MvcCore\Ext\Auths\Basic`	- always loaded
@param array $configuration Optional configuration passed into method
`\MvcCore\Ext\Auths\Basic::__construct($configuration)`.
@return \MvcCore\Ext\Auths\Full|\MvcCore\Ext\Auths\Basic|\MvcCore\Ext\Auths\Basics\IAuth