vue project, use Wechat"s third-party website to scan the code to log in, according to the official document

• first step

   var obj = new WxLogin({
   self_redirect:true,
   id:"login_container", 
   appid: "", 
   scope: "", 
   redirect_uri: "",  //
    state: "",
   style: "",
   href: ""
   });
  

• the second step is to get the interface of access_token through the address + code redirected in the previous step.

  http: GET
  https://api.weixin.qq.com/sns/oauth2/access_token?appid=APPID&secret=SECRET&code=CODE&grant_type=authorization_code

what I don"t understand is that Wechat"s code-scanning authentication page does not have a specified callback function to accept the return of the backend, so how to obtain the backend-related data and token and return it to the vue page is directly redirected to the frontend page (url with parameters)?