public function generateAccessToken()
    {

        // $this->access_token = Yii::$app->security->generateRandomString() . '_' . time();
        $signer = new Sha256();
        $token = Yii::$app->jwt->getBuilder()->setIssuer(Yii::getAlias("@restIssuer"))// Configures the issuer (iss claim)
        ->setAudience(Yii::getAlias("@restAudience"))// Configures the audience (aud claim)
        ->setId(Yii::getAlias("@restId")+ strtotime(date('Y-m-d',time())), true)
            ->setExpiration(time() + Yii::$app->params['accessTokenExpire'])// Configures exp time
            ->setIssuedAt(time())// Configures the time that the token was issue (iat claim)

            ->sign($signer, Yii::$app->jwt->key)
            ->getToken(); // Retrieves the generated token
        //$this->auth_key=$this->id;
        $this->access_token = (string)$token;
    }