fix(copilot): match the completions override by host, not whole string

is_copilot_completions_host is asked about two different shapes: a bare base URL
when routing, and the base URL plus the path when attaching auth. Comparing
GITHUB_COPILOT_PROXY_URL by whole-string equality answered True for the first
and False for the second, so an operator gateway was routed to correctly and
then forwarded with no credentials -- a 401 on the one configuration that is the
documented remedy for a custom deployment.

Compare hosts instead, via a shared _url_host() that also tolerates a
scheme-less value, and use it for the configured-API-URL check so a hand-written
'api.githubcopilot.com' is still recognised as public rather than read as a
custom deployment.

Author: Tejas Chopra

headroom/copilot_auth.py

@@ -291,6 +291,18 @@ def reset_observed_completions_endpoint() -> None:
     _observed_completions_base_url = None
 
 
+def _url_host(value: str) -> str:
+    """Hostname for a URL, tolerating a scheme-less value.
+
+    Mirrors the normalization :func:`is_copilot_api_url` performs, so a host
+    configured without "https://" is not silently treated as a different host.
+    """
+
+    parsed = urlparse(value)
+    netloc_or_path = parsed.netloc.lower() or parsed.path.lower()
+    return (parsed.hostname or netloc_or_path.split("/", 1)[0]).lower()
+
+
 def is_copilot_completions_host(url: str | None) -> bool:
     """Return True when *url* already points at a Copilot inline-completions host.
 
@@ -302,17 +314,17 @@ def is_copilot_completions_host(url: str | None) -> bool:
 
     if not url:
         return False
-    override = os.environ.get("GITHUB_COPILOT_PROXY_URL", "").strip().rstrip("/")
-    if override and url.rstrip("/") == override:
-        return True
-    # Tolerate a scheme-less value the same way ``is_copilot_api_url`` does; a
-    # configured host without "https://" must not silently stop being Copilot,
-    # because the consequence is a request forwarded without credentials.
-    parsed = urlparse(url)
-    netloc_or_path = parsed.netloc.lower() or parsed.path.lower()
-    host = (parsed.hostname or netloc_or_path.split("/", 1)[0]).lower()
+    # Compare hosts, never whole strings: this is asked both about a bare base
+    # URL (routing) and about a fully-built URL with the path appended (auth).
+    # A string compare answers True for the first and False for the second, so
+    # an operator override would route correctly and then be forwarded with no
+    # credentials at all.
+    host = _url_host(url)
     if not host:
         return False
+    override = os.environ.get("GITHUB_COPILOT_PROXY_URL", "").strip()
+    if override and host == _url_host(override):
+        return True
     if host == "copilot-proxy.githubusercontent.com":
         return True
     # Per-SKU hosts GitHub hands out via `endpoints.proxy`, e.g.
@@ -353,9 +365,7 @@ def copilot_completions_base_url() -> str:
     if _observed_completions_base_url:
         return _observed_completions_base_url
     configured = _configured_api_url_override()
-    if configured and not _is_public_copilot_api_host(
-        (urlparse(configured).hostname or "").lower()
-    ):
+    if configured and not _is_public_copilot_api_host(_url_host(configured)):
         return configured
     return DEFAULT_COMPLETIONS_PROXY_URL
 

tests/test_copilot_vscode_completions_routing.py

@@ -485,3 +485,64 @@ def test_a_custom_deployment_still_keeps_its_own_host(
     monkeypatch.setenv("GITHUB_COPILOT_API_URL", configured_api_url)
 
     assert copilot_completions_base_url() == configured_api_url
+
+
+# --------------------------------------------------------------------------- #
+# The two callers pass different shapes of URL
+# --------------------------------------------------------------------------- #
+def test_an_operator_override_is_matched_on_the_full_request_url(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Routing sees a base URL; auth sees the base URL *plus the path*.
+
+    Matching the override by whole-string equality answered True for the first
+    and False for the second, so an operator gateway was routed to correctly and
+    then forwarded with no credentials — a 401 on the one configuration that is
+    the documented remedy for a custom deployment.
+    """
+    monkeypatch.setenv("GITHUB_COPILOT_PROXY_URL", "https://gw.corp.internal")
+
+    base = "https://gw.corp.internal"
+    full = f"https://gw.corp.internal{COMPLETIONS}"
+
+    assert copilot_auth.is_copilot_completions_host(base) is True
+    assert copilot_auth.is_copilot_completions_host(full) is True
+    assert copilot_auth.is_copilot_completions_host("https://gw.corp.internal/") is True
+    assert copilot_auth.is_copilot_upstream_url(full) is True
+    # A different host is still not the override.
+    assert copilot_auth.is_copilot_completions_host(f"https://elsewhere.test{COMPLETIONS}") is False
+
+
+def test_an_operator_override_gateway_receives_credentials(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """End of the same chain: the gateway must actually be authenticated."""
+
+    class _Token:
+        token = "test-copilot-token"
+
+    class _Provider:
+        async def get_api_token(self):  # noqa: ANN202
+            return _Token()
+
+    monkeypatch.setenv("GITHUB_COPILOT_PROXY_URL", "https://gw.corp.internal")
+    monkeypatch.setattr(copilot_auth, "get_copilot_token_provider", lambda: _Provider())
+
+    resolved = asyncio.run(
+        copilot_auth.apply_copilot_api_auth({}, url=f"https://gw.corp.internal{COMPLETIONS}")
+    )
+
+    assert resolved.get("Authorization") == "Bearer test-copilot-token"
+
+
+@pytest.mark.parametrize(
+    "configured",
+    ["api.githubcopilot.com", "api.business.githubcopilot.com"],
+)
+def test_a_scheme_less_public_capi_url_is_still_recognised(
+    monkeypatch: pytest.MonkeyPatch, configured: str
+) -> None:
+    """A hand-written value without "https://" must not read as a custom host."""
+    monkeypatch.setenv("GITHUB_COPILOT_API_URL", configured)
+
+    assert copilot_completions_base_url() == COMPLETIONS_PROXY