How can I track uploads for a specific user?

Use Assembly fields to attach correlation metadata, such as a user ID or your application’s upload reference. With Uppy’s Transloadit plugin⁠, use assemblyOptions to obtain params, signature and optional fields from your backend.

For example, assemblyOptions.fields: { user_id: 'user-123' } makes the value available as ${fields.user_id} in instructions and in the fields object in Assembly Status. See fields in Templates.

Uppy sends these fields as separate multipart parts, outside the serialized params string. They are client-controlled. Even a field inside signed params.fields can be replaced in the merged fields by a later multipart field with the same name. Do not use returned fields alone to authenticate a user, choose an authorized storage destination or grant access to results.

For an association controlled by your application, follow verifying an upload’s user.