Use a different domain for SSL

long time lurker – first time poster.

A client of mine has a website developed in CakePHP, and a wordpress blog installed in the /blog/ directory.

Let’s say the url of the main domain is http://www.realdomain.com, with the blog being http://www.realdomain.com/blog/.

They don’t have their own SSL certificate so they use my companies. Let’s say the secure URL is https://realdomain.maindomain.net/blog/

I have the following code in my wp-config.php file:

define('WP_SITEURL', 'https://realdomain.maindomain.net/blog');
define('WP_CONTENT_URL', 'http://www.realdomain.com/blog/wp-content');
define('FORCE_SSL_LOGIN', true);
define('FORCE_SSL_ADMIN', true);

When I go to the /wp-login.php, it redirects me to the secure URL which is perfect.

However, when I log in to the secure site, WordPress tries to loads JavaScripts and styles from

`http**s**://realdomain.com`

Which causes problems because the main site doesn’t have a SSL certificate and as a result doesn’t load anything from https://realdomain.com

Is there anything else I’m missing?

Is the solution a .htaccess rule?
A rule which routed all “https://realdomain.com” to "https://realdomain.maindomain.com“?

I’ll pay anyone $20 who can help me fix it. I’ve Google’d until my hearts content and I don’t know what else I can do.

Thanks so much!

Just to keep things nice & clear, I’ve posted this as a new answer. Let’s reset the playing field & follow the below instructions as if it were a shiny new install (ignore all code & suggestions in previous answers).

In your wp-config.php

define( 'WP_SITEURL', 'http://www.realdomain.com/blog' );
define( 'SSL_DOMAIN_ALIAS', 'realdomain.maindomain.net' );

define( 'FORCE_SSL_LOGIN', true );
define( 'FORCE_SSL_ADMIN', true );

And in wp-content/mu-plugins/ssl-domain-alias.php

<?php

/**
 * Plugin Name: SSL Domain Alias
 * Plugin URI: http://wordpress.stackexchange.com/questions/38902
 * Description: Use a different domain for serving your website over SSL, set with <code>SSL_DOMAIN_ALIAS</code> in your <code>wp-config.php</code>.
 * Author: TheDeadMedic
 * Author URI: http://wordpress.stackexchange.com/users/1685/thedeadmedic
 *
 * @package SSL_Domain_Alias
 */

/**
 * Swap out the current site domain with {@see SSL_DOMAIN_ALIAS} if the
 * protocol is HTTPS.
 *
 * This function is not bulletproof, and expects both {@see WP_SITEURL} and
 * {@see SSL_DOMAIN_ALIAS} to be defined.
 *
 * @todo The replacement is a simple string replacement (for speed). If the
 * domain name is matching other parts of the URL other than the host, we'll
 * need to switch to a more rigid regex.
 *
 * @param string $url
 * @return string
 */
function _use_ssl_domain_alias_for_https( $url )
{
    static $domain;
    if ( ! isset( $domain ) )
        $domain = defined( 'WP_SITEURL' ) && defined( 'SSL_DOMAIN_ALIAS' ) ? parse_url( WP_SITEURL, PHP_URL_HOST ) : false;

    if ( $domain && strpos( $url, 'https' ) === 0 )
        $url = str_replace( $domain, SSL_DOMAIN_ALIAS, $url );

    return $url;
}
add_filter( 'plugins_url', '_use_ssl_domain_alias_for_https', 1 );
add_filter( 'content_url', '_use_ssl_domain_alias_for_https', 1 );
add_filter( 'site_url', '_use_ssl_domain_alias_for_https', 1 );

?>

I’ve suggested using a Must-Use plugin (mu-plugins), since these are autoloaded without having to be activated first.

If you’d rather it be a standard plugin, you’ll need to add the FORCE_SSL_* constants after activation.