feat: honor NO_GCE_CHECK environment variable

google/auth/compute_engine/_metadata.py

@@ -60,6 +60,10 @@
 except ValueError:  # pragma: NO COVER
     _METADATA_DEFAULT_TIMEOUT = 3
 
+# This is used to disable checking for the GCE metadata server and directly
+# assuming it's not available.
+_NO_GCE_CHECK = os.getenv(environment_vars.NO_GCE_CHECK) == "true"
+
 # Detect GCE Residency
 _GOOGLE = "Google"
 _GCE_PRODUCT_NAME_FILE = "/sys/class/dmi/id/product_name"
@@ -75,6 +79,9 @@ def is_on_gce(request):
     Returns:
         bool: True if the code runs on Google Compute Engine, False otherwise.
     """
+    if _NO_GCE_CHECK:
+        return False
+
     if ping(request):
         return True
 

google/auth/environment_vars.py

@@ -60,6 +60,12 @@
 """Environment variable providing an alternate ip:port to be used for ip-only
 GCE metadata requests."""
 
+NO_GCE_CHECK = "NO_GCE_CHECK"
+"""Environment variable controlling whether to check if running on GCE or not.
+
+The default value is false. Users have to explicitly set this value to true
+in order to disable the GCE check."""
+
 GOOGLE_API_USE_CLIENT_CERTIFICATE = "GOOGLE_API_USE_CLIENT_CERTIFICATE"
 """Environment variable controlling whether to use client certificate or not.
 

tests/compute_engine/test__metadata.py

@@ -83,6 +83,20 @@ def test_is_on_gce_ping_success():
     assert _metadata.is_on_gce(request)
 
 
+def test_is_on_gce_no_gce_check():
+    request = make_request("", headers=_metadata._METADATA_HEADERS)
+
+    os.environ[environment_vars.NO_GCE_CHECK] = "true"
+    importlib.reload(_metadata)
+
+    try:
+        assert not _metadata.is_on_gce(request)
+        assert request.call_count == 0
+    finally:
+        del os.environ[environment_vars.NO_GCE_CHECK]
+        importlib.reload(_metadata)
+
+
 @mock.patch("os.name", new="nt")
 def test_is_on_gce_windows_success():
     request = make_request("", headers={_metadata._METADATA_FLAVOR_HEADER: "meep"})