Either try to work out how to pass headers through to get around the service login or give up and find another app. On some services, the service auto logs onto one account so anybody who gets through Authentik sees the same stuff which is fine. I definitely don’t have two levels of login!
I should say I use Plex’s and vaultwarden’s own login systems.
I have a reason I don’t think is covered. A few programs I have come across that I want to try recommend docker and some only provide instructions for docker. They can spend less time trying to help you with dependencies and installations knowing they’ve included everything you need in the docker file. I don’t have a background in Linux or programming so unless they tell you exactly how to install something, I can struggle. Their installation page is then just the docker compose file with a note on the environment variables you can change.