Unable to access admin with ssl

Hi there!

I just passed my website on https. After a bit difficult configuration (on Apache with Nginx reverse proxy), everything seemed okay.

The problem lay in the admin panel. I can login without any problem, and I see that i’m logged in when viewing the website, but i can’t access to admin panel. I get this error :

You don’t have the rights to access this page.

I’m the only user, so i’m the administrator for sure.

I added this bit to wp-config.php:
define('FORCE_SSL_ADMIN', true);

If I remove it, I get this error in the logs:

PHP Fatal error:  Uncaught Error: Call to undefined function nocache_headers() in /var/www/emmanuelbeziat/site/wp-admin/admin.php:33
Stack trace:
#0 /var/www/emmanuelbeziat/site/wp-admin/index.php(10): require_once()
#1 {main}
thrown in /var/www/emmanuelbeziat/site/wp-admin/admin.php on line 33

Here’s the vhost in Apache:

<VirtualHost 127.0.0.1:8082>
    ServerName www.emmanuelbeziat.com
    ServerAlias www.emmanuelbeziat.com
    ServerAdmin contact@emmanuelbeziat.com

    DocumentRoot /var/www/emmanuelbeziat/site

    ErrorLog ${APACHE_LOG_DIR}/emmanuelbeziat/site_error.log
    CustomLog ${APACHE_LOG_DIR}/emmanuelbeziat/site_access.log combined

    # Configuration WordPress
    <Directory "var/www/emmanuelbeziat/site">
        <IfModule mod_rewrite.c>
            RewriteEngine On
            RewriteBase /
            RewriteRule ^index\.php$ - [L]
            RewriteCond %{REQUEST_FILENAME} !-f
            RewriteCond %{REQUEST_FILENAME} !-d
            RewriteRule . /index.php [L]
        </IfModule>
    </Directory>

    # Protection du fichier wp-config
    <Files wp-config.php>
        Require all denied
    </Files>
</VirtualHost>

And in Nginx:

server {
    listen    443 ssl;
    server_name    www.emmanuelbeziat.com;
    access_log    /var/log/nginx/emmanuelbeziat/emmanuelbeziat.access.log;
    error_log    /var/log/nginx/emmanuelbeziat/emmanuelbeziat.nginx_error.log info;

    access_log    off;
    location = /favicon.ico    { access_log off; log_not_found off; }
    location / {
        proxy_pass http://127.0.0.1:8082/;
        include /etc/nginx/conf.d/proxy.conf;
        root /var/www/emmanuelbeziat/site;
    }

    location ~* ^.+.(jpg|jpeg|gif|css|png|js|ico|txt|srt|swf)$ {
        root /var/www/emmanuelbeziat/site/;
        expires 30d;
    }

    ssl_certificate /etc/letsencrypt/live/emmanuelbeziat.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/emmanuelbeziat.com/privkey.pem;

}

server{
    listen 80;
    server_name emmanuelbeziat.com www.emmanuelbeziat.com;

    location / {
        rewrite ^(.*)$ https://www.emmanuelbeziat.com$1 permanent;
    }
}

And here’s a phpinfo() with some stuff.

If you need more configuration file, i’ll put it up here.

If someone have and idea, thanks in advance!