Customization of openid-configuration

Hi, I have a private instance of gitlab free tier running and wanted to use it as an OpenID provider for some internal applications. I followed the instructions provided here and in its sub-pages. It’s “almost” working but I encountered the following issue: The endpoints in /well-known/openid-configuration are not correct.

The gitlab instance is hosted on an http path (in the following, http://gitlab.example.lan). In the openid-configuration, this is correctly represented in the issuer field. However, all other fields (e.g. authorization_endpoint, token_endpoint, etc.) point to an https path, e.g. https://gitlab.example.lan/oauth/token. Since this path does not exist, the authentication workflow fails.

I checked the admin panel but I could not find a way to adjust this. Can it be manually adjusted? What steps are necessary to do so?

The server is running Gitlab 15.9.