Uploading files to a separate server, and missing data about the uploader

Question

I am using two servers:

1. Elixir
2. tus-node-server

because tus-node-server is an official implementation of the tus protocol.

the issue is that the tus-node-server has no data about the users,

so when User 1 uploads File 1,

User 1 is only authenticated to elixir server and not to the tus-node-server, so there is no way to give User 1 any extra permissions on that file that he uploaded.

How can you add User 1 information to the uploaded files?