Add SPOG (Custom URL) routing support via x-databricks-org-id header

[msrathore-db]

Summary

On SPOG (Custom URL / account-level) workspaces, httpPath has the form /sql/1.0/warehouses/<id>?o=<workspaceId>. The ?o= parameter routes Thrift calls correctly via the URL, but other endpoints (telemetry push, feature-flag check) run on separate hosts and need x-databricks-org-id as an HTTP header to route to the right workspace. Without it, those requests 404 or get misrouted on SPOG hosts.

Change

All contained in connector.go:

1. extractSpogHeaders(httpPath string) map[string]string — parses the ?o= query param using url.ParseQuery (stdlib, not regex). Returns {"x-databricks-org-id": "<workspaceId>"} or nil. Three DEBUG log paths cover: malformed query, missing ?o=, and successful extraction.

2. headerInjectingTransport — a lightweight http.RoundTripper wrapper that clones the request per the contract and sets the provided headers if not already set by the caller.

3. withSpogHeaders(base *http.Client, headers map[string]string) *http.Client — returns a new client with the same settings but a wrapped transport.

4. In Connect(), when extractSpogHeaders returns non-nil, the driver passes a wrapped client into TelemetryInitOptions.HTTPClient. The wrapped client is used for both the feature-flag check and the telemetry push. The driver's own c.client is left alone, so Thrift routing (which uses ?o= in the URL) is unaffected.

Why a transport wrapper instead of threading a parameter

An earlier revision of this PR threaded an extraHeaders parameter through telemetry.TelemetryInitOptions → isTelemetryEnabled → featureFlagCache.isTelemetryEnabled → fetchFeatureFlag. That approach:

• Required API-surface changes in 3 telemetry files (config.go, featureflag.go, driver_integration.go).
• Only covered the feature-flag check; telemetry/exporter.go (telemetry push) still sent Content-Type as the only header — SPOG routing would 404 at push time.

The RoundTripper wrapper:

• Keeps telemetry/* identical to origin/main. Zero API churn.
• Automatically applies to every outbound request using the wrapped client — feature-flag check, telemetry push, and any future HTTP paths that reuse it.
• Respects caller-set headers (if a request already has x-databricks-org-id for some reason, the wrapper does not override).

Endpoints covered

Endpoint	Uses wrapped client?	Gets x-databricks-org-id?
Feature flags /api/2.0/connector-service/feature-flags/GOLANG/{v}	Yes	✅
Telemetry push	Yes	✅
Thrift	No (uses c.client directly; already routes via URL)	— (not needed — URL-routed)
OAuth token exchange	No (separate client, talks to login.microsoftonline.com)	— (not needed)
CloudFetch / Volume operations	No (presigned URLs)	— (not needed)

Verification

• go build ./... clean.
• Debug log output confirms extraction on SPOG URLs:

  SPOG header extraction: injecting x-databricks-org-id=<id> (extracted from ?o= in httpPath)
  

Note on the earlier auth/oauth/u2m/u2m.go change

The two earliest commits on this branch (23697e5, 0ec7e06) modified auth/oauth/u2m/u2m.go to avoid sending an empty client_secret on the PKCE public-app flow, documented as a fix for the server's "Public app should not use a client secret" rejection. That change was empirically verified to not be needed (see commit 3576c92 which reverts it):

• Prod Legacy (adb-6436897454825492.12.azuredatabricks.net): Unpatched u2m.go PASSES end-to-end. Server accepts the empty client_secret.
• Stg Legacy (adb-7064161269814046.2.staging.azuredatabricks.net): Unpatched u2m.go FAILS with unexpected HTTP status 400 Bad Request during token exchange.

Since production tolerates the current behavior, customers aren't impacted. Keeping this PR minimal; if staging-level strictness later rolls out to prod, we can re-add the u2m fix then.

Test plan

• Unit tests pass (go test ./...)
• Manually verified SPOG header injection appears in x-databricks-org-id on feature-flag check and telemetry push against a SPOG workspace (not gated by this PR, but prerequisite for SPOG telemetry to work at all)
• No regressions on non-SPOG workspaces (wrapper is a no-op when extractSpogHeaders returns nil)

[samikshya-db]

Thanks for this, please add in nodejs too 🙏