Post Preview not working behind Proxy

Hi all,

I′ve got a Problem with the post/page preview in WordPress.

The Serve-Configuration is as follow:

The WordPress address is set to sub2.example.com (IP: 123.12.1.2),
and the site URL is set to sub1.example.com (IP: 123.12.1.1).

Both IPs directs to the same server, for each IP there is an own Apache-Instance running.

If a Client requests the site sub1.example.com, this “server” requests the wordpress site from sub2.example.com, transforms the output and finally send the transformed output to the requesting client:

+--------+      +------------------+       +------------------+
|        | ---> | sub1.example.com | --->  | sub2.example.com |
| CLIENT |      |                  |       |                  |
|        | <--- | IP 123.12.1.1    | <---  | IP: 123.12.1.2   |
+--------+      +------------------+       +------------------+
                  Transforms the                WordPress
                  WordPress output

This works as it should, but now comes my problem:

The WordPress admin area is accessible via sub2.example.com/wordpress/wp-admin.
When I edit a post or a page and click on PREVIEW, I get redirected, for example, to https://sub1.example.com/hello-world/?preview=true&preview_id=1&preview_nonce=1234567890.
And this redirect fails: “You do not have the necessary rights to see the preview”.

(If I call https://sub2.example.com/hello-world/?preview=true&preview_id=1&preview_nonce=1234567890 it works pretty fine, but i need to call sub1.example.com …)

First i thought that this is a Problem with the WordPress authentication cookie, so i installed the Root Cookie Plugin. The cookie, wich is set for sub1.example.com contains :

• name: wordpress_logged_in_919292837291837382927,
  value: admin%8289328%9324789347843789,
  Domain: .example.com,
  path: /
• name: wordpress_919292837291837382927,
  value: admin%82893289324%789347843789,
  Domain: .example.com,
  path: /

But this didn′t solve my Problem, I still get the same error.

Some other attempts i′ve tried:

• Setup sub1.example.com as Proxy Server:

  define('WP_PROXY_HOST', '123.12.1.1');
  define('WP_PROXY_PORT', '80');
  define('WP_PROXY_USERNAME', '');
  define('WP_PROXY_PASSWORD', '');
  define('WP_PROXY_BYPASS_HOSTS', 'localhost');

But this also did not work.

I hope you understand my problem and maybe someone has an idea how to solve this?

Thanks in advanced and sorry for my bad english (this is not my native language ?? )

(I also posted this question at https://wordpress.stackexchange.com and https://stackoverflow.com)