HTTPS reverse proxy redirect loop

Hi,

I have tried everything I have found on the support forums and around the Internet but to no avail (running WordPress 4.1.1). Follows a description of the configuration. I can only access the HTTPS reverse proxied WordPress installation if in “wp-config.php”, I set the $_SERVER[‘HTTP_HOST’] variable to NULL (see bellow).

1. WordPress
1.1. Site URL: https://www.external.domain (configuration in database)
1.2. Home: https://www.external.domain (configuration in database)
1.3. Reverse proxy related code in “config-wp.php”
if (!empty($_SERVER[‘HTTP_X_FORWARDED_HOST’])) {
//$_SERVER[‘HTTP_HOST’] = NULL;
$_SERVER[‘HTTP_HOST’] = $_SERVER[‘HTTP_X_FORWARDED_HOST’];
}

// Need to add IPv6 support
if (!empty($_SERVER[‘HTTP_X_REAL_IP’]) && preg_match( ‘/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/’, $_SERVER[‘HTTP_X_REAL_IP’])) {
$_SERVER[‘REMOTE_ADDR’] = $_SERVER[‘HTTP_X_REAL_IP’];
}

if (!empty($_SERVER[‘HTTP_X_FORWARDED_PROTO’]) && $_SERVER[‘HTTP_X_FORWARDED_PROTO’] === ‘https’) {
$_SERVER[‘HTTPS’] = ‘on’;
}

2. NGINX
2.1. Frontend HTTPS termination configuration
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_pass https://www.internal.domain;

2.2. Backend HTTP configuration
try_files $uri =404;
fastcgi_pass unix:/var/run/php-fpm/php-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;

3. Example communication from reverse proxy to backend
3.1. Request
GET /index.php HTTP/1.0
X-Real-IP: xxx.xxx.xxx.xxx
X-Forwarded-Host: https://www.external.domain
X-Forwarded-For: xxx.xxx.xxx.xxx
X-Forwarded-Proto: https
Host: https://www.internal.domain
Connection: close
User-Agent: (…)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: (…)

3.2. Response
HTTP/1.1 301 Moved Permanently
Server: nginx
Date: Thu, 16 Apr 2015 10:44:58 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
X-Pingback: https://www.external.domain/xmlrpc.php
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Pragma: no-cache
Location: https://www.external.domain/

What the hell am I doing wrong or have I missed??