There is a solution for id Tech 4 master server by Xanz: https://github.com/Xanz/XanzMasterServer/tree/main
Xanz could help with this solution if you decide to implement it in the OpenSpy codebase.
I understand that OpenSpy is a GameSpy replacement and none of the ID games used that technology. However, a lot of players would benefit of migrating to OpenSpy because GOG versions of id Tech 4 games, specifically Quake 4 do not work properly with the ID's master server.
There is a solution for id Tech 4 master server by Xanz: https://github.com/Xanz/XanzMasterServer/tree/main
Xanz could help with this solution if you decide to implement it in the OpenSpy codebase.
I understand that OpenSpy is a GameSpy replacement and none of the ID games used that technology. However, a lot of players would benefit of migrating to OpenSpy because GOG versions of id Tech 4 games, specifically Quake 4 do not work properly with the ID's master server.