How to make a custom dependency source optional?

[Kludex]

Hi there 👋

I have a custom dependency source on an open source project:

[[tool.rye.sources]]
name = "company-internal"
url = "https://${INDEX_USERNAME}:${INDEX_PASSWORD}@potato.pydantic.dev/simple/"

If I don't have the INDEX_USERNAME and the INDEX_PASSWORD in the environment, then it fails with 401:

❯ rye sync
Reusing already existing virtualenv
Generating production lockfile: /Users/marcelotryle/dev/pydantic/logfire/requirements.lock
error: Failed to build editables
  Caused by: Failed to build editable: file:///Users/marcelotryle/dev/pydantic/logfire
  Caused by: Failed to install requirements from build-system.requires (resolve)
  Caused by: No solution found when resolving: hatchling
  Caused by: HTTP status client error (401 Unauthorized) for url (https://pppr.pydantic.dev/simple/hatchling/)
error: could not write production lockfile for project

Caused by:
    Failed to run uv compile /var/folders/83/j6hy2y7d38s5m1lhn7lz16180000gn/T/.tmpXPM2fP/requirements.txt. uv exited with status: exit status: 2

Is there a way to have that source optional? I'm using that index for MkDocs Insiders packages - alternative suggestions on how to do it are welcome.