Trying to setup a main reverse proxy in front of Authentik backend - Getting error 400

[l3ochan]

Hello everyone, I'm trying to setup a frontal reverse proxy, that will have a WAF and some other security features to better protecy my homelab from the outside world.
The current setup I have is an authentik instance running in docker on a server that is my backend.
My backend has an apache reverse proxy that allows TLS encryption between the backend and frontal web server.

The issue that I have is that when I try to access Authentik with this setup, I'm getting an HTTP error 400.

Config for my backend:

<VirtualHost *:80>
    ServerName sso.local
    RewriteEngine on
    RewriteCond %{SERVER_NAME} =sso.local
    RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
    ServerSignature Off
    CustomLog /var/log/apache2/sso.local_access.log access_logs
    ErrorLog /var/log/apache2/sso.local_error.log
</VirtualHost>

<VirtualHost *:443>
    ServerName sso.local
    RemoteIPHeader "%{REMOTE_ADDR}s"
    ProxyPreserveHost On
    SSLProxyVerify none
    SSLProxyCheckPeerCN off
    SSLProxyCheckPeerName off
    SSLProxyCheckPeerExpire off
    SSLProxyEngine on
    ProxyPass "/" "https://127.0.0.1:9092/" upgrade=websocket
    ProxyPassReverse "/" "https://127.0.0.1:9092/"
    RequestHeader set Origin "https://sso.domain.tld"
    RequestHeader set X-Forwarded-For "%{REMOTE_ADDR}s"
    RequestHeader set X-Forwarded-Proto "https"

    CustomLog /var/log/apache2/sso.local_access.log access_logs
    ErrorLog /var/log/apache2/sso.sso.local_error.log
    ServerSignature Off
Include /etc/letsencrypt/options-ssl-apache.conf
SSLCertificateFile /path/to/cert
SSLCertificateKeyFile /path/to/key
</VirtualHost>

Config for the frontal reverse proxy