This is based on authentik 2021.10.3 and Gitea 1.16.0+rc1 installed using https://docs.gitea.io/en-us/install-from-binary/. Instructions may differ between versions.
In authentik, create an application (under _Resources/Applications_) which uses this provider. Optionally apply access restrictions to the application using policy bindings.
:::note
Only settings that have been modified from default have been listed.
`Add Authentication Source` and you should be done. Your Gitea login page should now have a `Sign in With` followed by the authentik logo which you can click on to sign-in to Gitea with Authentik creds.