fix: Preserve Azure authentication boundaries across transports (#3684)

## Summary
Keep Azure authentication scoped to the original request origin across
HTTP and Realtime connections. Supported HTTP clients remove the Azure
API key when following an off-origin redirect, and async Realtime
connections reject off-origin handshake redirects. Same-origin
authentication and normal connection behavior remain intact.

The change is limited to Azure transport handling and focused
synchronous/asynchronous coverage for stable and beta Realtime. No
public API or dependency changes.