Accessing authentication token in callbacks

I am creating a plotly dash site that will be hosted on another site via an iframe, the other site also handles authentication. It then sends a authentication token in the header of the request to the plotly dash site. Then in a callback the plotly dash site is supposed to download data from a database and display it. What data exactly is downloaded depends on the token. But i have a problem getting the token from the first GET-request to the callback so it can download the correct data.
Thank you in advance