openvpn-auth-oauth2 asks for OIDC issuer even though the oauth2.endpoint.discovery is set

### Current Behavior When the `oauth2.endpoint.discovery` is set (we are using environment variables) `openvpn-auth-oauth2` fails to start and complains that `oauth2.issuer` is not set. This is strange since the issuer is present in the discovery metadata ### Expected Behavior If `oauth2.endpoint.discovery` is set, the program should not demand that `oauth2.issuer` is set ### Steps To Reproduce ```Markdown root@1fe207dd7b43:/# env|grep DISCOVERY CONFIG_OAUTH2_ENDPOINT_DISCOVERY=https://host.docker.internal:8443/cas/oidc/.well-known/openid-configuration root@1fe207dd7b43:/# env|grep ISSUER CONFIG_OAUTH2_ISSUER=https://host.docker.internal:8443/cas/oidc root@1fe207dd7b43:/# unset CONFIG_OAUTH2_ISSUER root@1fe207dd7b43:/# env|grep ISSUER root@1fe207dd7b43:/# openvpn-auth-oauth2 configuration validation error: oauth2.issuer is required # export CONFIG_OAUTH2_ISSUER=https://host.docker.internal:8443/cas/oidc openvpn-auth-oauth2 starts ``` ### Environment - openvpn-auth-oauth2 Version: 1.26.4 - OpenVPN Server Version: 2.6.3-1+deb12u4 - Server OS: Debian 12 (bookworm) - OpenVPN Client (flavor, OS): OpenVPN Connect - OIDC Provider: Apereo CAS ### openvpn-auth-oauth2 logs ```shell configuration validation error: oauth2.issuer is required ``` ### openvpn server logs ```shell ``` ### Anything else? _No response_ ### Preflight Checklist - [x] I could not find a solution in the [documentation](https://github.com/jkroepke/openvpn-auth-oauth2/wiki), the [FAQ](https://github.com/jkroepke/openvpn-auth-oauth2/wiki/FAQ), the existing issues or discussions.