Sourcegraph extension not loading on GHE

Created by: dadlerj

• Sourcegraph version: 3.6
• Platform information: Chrome extension on GHE

Steps to reproduce:

Reported by https://app.hubspot.com/contacts/2762526/company/768958849

A customer authored an extension and published it to their private extension registry.

It works on their internal Sourcegraph instance, but on their GitHub Enterprise instance, they see the following error in the console:

Error fetching extension script URL https://sourcegraph.example.com/-/static/extension/... Error: ajax error 401

extensionsService.ts:160

at a.bind.resolve (browser-polyfill.js:1118)