How to setup SSL with port other than 443

My version of HedgeDoc is: 1.9.9

What I expected to happen:

I tried to setup HedgeDoc 1.9.9 with reverse proxy over SSL, and I want to use port 8000 other than default 443, as port 443 is forbidden by my IT policy.

What actually happened:

My Apache conf:

Listen 8000
SSLCryptoDevice builtin
<VirtualHost *:8000>

  ErrorLog        /var/log/httpd/hedge_error_log.txt
  TransferLog     /var/log/httpd/hedge_access_log.txt

  LogLevel warn
  SSLEngine on
  SSLProxyEngine on

  RewriteEngine on
  RewriteCond %{REQUEST_URI} ^/             [NC]
  RewriteCond %{HTTP:Upgrade} =websocket             [NC]
  RewriteRule /(.*)  ws://$1          [P,L]

  ProxyPass /
  ProxyPassReverse /

  RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}

  SSLCertificateFile      conf/ssl/		##self assigned certificate
  SSLCertificateKeyFile   conf/ssl/


I already tried:

I tried to modify config.json as: “domain”: “”, and can create guest notes.
But failed to register new user: after input email and password and click Register button, no user created and cannot sign in.

My HedgeDoc config.json:

"production": {
        "domain": "",
        "loglevel": "info",
        "cookiePolicy": "lax",
        "db": {
            "username": "xxxxxx",
            "password": "xxxxxx",
            "database": "hedgedoc",
            "host": "",
            "port": "3306",
            "dialect": "mariadb"

        "linkifyHeaderStyle": "gfm"