How can I access
$_POST data after a page redirect?
I guess there is some way to tell WordPress to pass all
$_POST data to the redirected address, like it does with
$_GET data, using Rewrite Rules, but how?
Redirects are GET requests usually, and the browser doesn’t send the POST data for those. That’s not something WordPress can change.
You could create a session, or – better – process the POST data first, then redirect. In your plugin, you could do: