Write script to link `hedgedoc` SAML auth to `authentik`

[pirate]

When all the containers first come up, there are in an empty clean slate state.

Please write a script that creates whatever config files & db records are needed to point HedgeDoc to Authentik for authentication.

The code should live in either hedgedoc/bin/link_to_authentik.sh and/or authentik/bin/link_to_hedgedoc, whatever you think describes it best. The script should take the following inputs as environment variables:

• COMPANY_NAME=SelfHostYourTech
• COMPANY_DOMAIN=selfhostyour.tech
• ADMIN_USERNAME=admin
• ADMIN_PASSWORD=<random if not provided>

It should programatically perform the steps described here on the HedgeDoc side and the Authentik side:

• https://docs.hedgedoc.org/guides/auth/saml/
• https://docs.goauthentik.io/docs/add-secure-apps/providers/saml/

You can write directly to the apps data in ./<appname>/data/..., you can use their REST/RPC APIs, you can add config by writing to .env in the app dirs, the only thing the script cant do is require the user to click around in any UIs.

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Subtasks

• Make sure ./authentik/docker-compose.yml works to spin up a fresh empty autentik server
• Make sure ./hedgedoc/docker-compose.yml works to spin up a fresh empty HedgeDoc server
• Make sure you can access the REST APIs / endpoints / filesystems of both as needed to automate the setup process