Classic API — Authentication

The Classic API is a control-plane surface. Document its auth scheme here.

Stub — confirm against source.

Capture the exact auth model from the cloud_control_plane monolith implementation and verify it against the "Security" section of the Stoplight reference. Do not guess credentials here.

• Never put credentials in client-side code or URLs.
• Prefer linking to the owning repo's auth docs over duplicating them.