Where to get the Authentication Token for a Headless Server?

[SuperProPlayer]

I've been looking for it without much luck.

[daniel34]

The token that goes into the server-settings.json file? You can find it in %appdata%\Factorio\player-data.json under the name service-token.

You'll need to be logged in already (in the game) for that to work, because once you log in (when searching for mods or browsing multiplayer server) it will download the token for your user and save it in that file.