Assigning the property $action of a class ($this) to an variable $conf, why it is an array?

Question

There is the following function in the controller.php of framework thinkphp used in a project, where there is this line of codes: "$conf = $this->$action".

"if (property_exists($this, $action))" is checking if there exists property $action in the class $this. Form the next line of codes "if (key_exists('login', $conf))", it looks to me that $conf is an array.

My question is: what exactly is "$conf = $this->$action" doing, assigning an array (the property $action? why $action is an array?) to the variable $conf?

public function checkAccessControl()
        {
            if (Config::get('frame.controller.checkAccessControl.exec')) {
                $action = $this->request ->action(true);
                if (property_exists($this, $action)) {
                    $conf = $this->$action;
                    if (key_exists('login', $conf)) {
                        if ($conf['login'] === true && $this->if_login === false) {
                            $this->access_control_check = false;
                            $this->response(["error"=>"未登录用户无权访问"],[],401,'json');//要求用户的身份认证
                        } else {
                            $this->access_control_check = true;
                        }
                    } else {
                        $this->access_control_check = false;
                        $this->response(["error"=>"代码错误：未标注访问类型"],[],500);//服务器内部错误，无法完成请求（未在控制器中标注login的访问控制）
                    }
                } else {
                    $this->access_control_check = false;
                    $this->response(["error"=>"代码错误：未标注访问控制"],[],500,'json',['action'=>$this->request->action(true)]);//服务器内部错误，无法完成请求（未在控制器中标注方法的访问控制）
                }
            } else {
                $this->access_control_check = Config::get('frame.controller.checkAccessControl.default.access_control_check');

            }
        }