How can I achive this behavor in nginx

What is the configuration needed in Nginx to achieve the following behavior:

Whenever a request is received, it should be forwarded to application A; if application A returns { "allowed" :true} in response, the same request should be forwarded to application B and the response from application B should be returned to the client. However, if application A returns a { "allowed" : false} in response, the server should return a response with a status code of 401.

Something like this:

server {
   listen  80;

location / {
    # forword request to App-A;
    proxy_pass https://app-A.dev/;
    # Read the response
    if response['allowed'] == true;
        # forword it to application B
        proxy_pass https://app-B.dev/;
    else:
        return '401';
    }   
}

This: https://docs.nginx.com/nginx/admin-guide/security-controls/configuring-subrequest-authentication/

You can have a look at Authelia or Authentik for the authentication application.