Possible to fix admin URL behind proxy issue without hacking core?

I threw this question around on Twitter and asked for feedback from some other core developers. My gut instinct was to make $current_url either filterable or generated by a function that could be overridden. This is, apparently, the wrong way about it.

@markoheijnen:
@EricMann Resetting $_SERVER['HTTP_HOST'] sounds like a hackish solution. Same code then can be in wp-config.php

‏@nacin:
@EricMann @markoheijnen Putting it in wp-config is proper. It is not WP’s job to handle reverse proxy situations.

@EricMann @markoheijnen Ideally, they should be set properly before WP (or even PHP) is loaded. wp-config is the alternative.

@markoheijnen:
@nacin @ericmann In this case the server/proxy is wrong configured. So I can see why it then should be fixed in wp-config

From the sounds of this converation, you have two options:

1. Reconfigure your proxy to set the correct host values before things even get to PHP/WP.
2. Manually clean and set up $_SERVER['HTTP_HOST'] in your wp-config.php file.

---

I thought a bit more, and here’s some actual code you could add to wp-config.php to set things up (based on the hacky patch that changes core files):

if ( ! empty( $_SERVER['HTTP_X_FORWARDED_HOST'] ) ) {
    $_SERVER['HTTP_HOST'] = $_SERVER['HTTP_X_FORWARDED_HOST'];
}

This should set things up such that the default core files don’t need any modification to function correctly. But please note that I can’t test this since I don’t have any kind of proxy setup to verify it against … so if this code doesn’t help fix your situation, please report back and we can try something else.