Hello, I have two servers. On one I run a website called `example.com`

And at the moment I use the other server as a Nginx proxy. So I aimed the domain to the proxy server, which proxy passes the IP of the website server.

How can I implement a page on the proxy server to stop all incoming traffic and ask them for a simple captcha authentication? If the captcah is solved they will be proxy_passed to the IP of the other server, and will never see this page again. If they don't they will stay at the captcha page until they solve it. How can I do this?