https and Control Panel mixed content error

Question

I've got a site in SSL but when I visit the Control panel it is completely unstyled and looking in the inspector I see a mixed content error and js/css is being blocked.

Not sure why this is happening, but in case it's relevant am using FocusLab Master Config for EE3

**** UPDATE *****

I added this to config.prod.php and no change

$env_config['cp_url'] = 'https://www.domain.com/admin.php';

**** UPDATE 2 ****

This is in response to @jrothafer about the config settings. Here is the relevant code from config.master.php

$protocol = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on') ? 'https://' : 'http://';
$base_url = $protocol . $_SERVER['HTTP_HOST'];
$base_path = $_SERVER['DOCUMENT_ROOT'];

Answer 1

This is always a themes folder and protocol issue, I've found. You mentioned this:

$env_config['cp_url'] = $env_config['base_url'] . '/admin.php';

What are you parameters for various $env_config array entries? Make sure that array is using https for that URL, and also your themes folder must also be behind SSL.

Update

Hey, so are you forcing SSL for all connections? If not, you should be! Otherwise,

$protocol = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on') ? 'https://' : 'http://';
$base_url = $protocol . $_SERVER['HTTP_HOST'];
$base_path = $_SERVER['DOCUMENT_ROOT'];

This set up will respect the HTTP protocol request and load assets over plain HTTP. You need to force that SSL! Best using .htaccess rules, or equivalent nginx rules:

RewriteCond %{HTTP_HOST} ^mydomain\.com$ [NC]
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteRule ^(.*)$ https://mydomain.com/ [R=301,L]

Answer 2

With help from @jrothafers answer. I hardcoded the themes path in config.master.php and it's working now.

$env_config['theme_folder_url'] = https://www.domain.com/themes/';

Ideally I wouldn't have to do that, but it works.