Wiki.js is a wiki engine running on Node.js and written in JavaScript. It is free software released under the Affero GNU General Public License. It is available as a self-hosted solution or using "single-click" install on the DigitalOcean and AWS marketplace.
You do not have to enable "Allow self-registration" and select a group to which new users should be assigned, but if you don't you will have to manually provision users in Wiki.js and ensure that their emails match the email they have in authentik.
If you're using self-signed certificates for authentik, you need to set the root certificate of your CA as trusted in WikiJS by setting the NODE_EXTRA_CA_CERTS variable as explained here: https://github.com/Requarks/wiki/discussions/3387.
In authentik, create an application which uses this provider. Optionally apply access restrictions to the application using policy bindings.
Set the Launch URL to the _Callback URL / Redirect URI_ without the `/callback` at the end, as shown below. This will skip Wiki.js' login prompt and log you in directly.