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fix(auth): properly extract stdout from gnubby webauthn plugin failures #17885

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fix(auth): properly extract stdout from gnubby webauthn plugin failures #17885

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cb03c15
fix(auth): properly extract stdout from gnubby webauthn plugin failures
macastelaz Jul 23, 2026
74832cc
style(auth): format webauthn plugin files with black
macastelaz Jul 23, 2026
a40c49a
fix(auth): conditionally strip stdout bytes during fallback
macastelaz Jul 23, 2026
92bb6e0
test(auth): explicitly set mock returncode for older tests
macastelaz Jul 24, 2026
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21 changes: 18 additions & 3 deletions packages/google-auth/google/oauth2/webauthn_handler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -57,9 +57,24 @@ def _call_plugin(self, cmd: str, input_json: str) -> str:
request = length_bytes_le + input_json.encode()

# Call plugin
process_result = subprocess.run(
[cmd], input=request, capture_output=True, check=True
)
process_result = subprocess.run([cmd], input=request, capture_output=True)

if process_result.returncode != 0:
stdout_bytes = process_result.stdout
if (
len(stdout_bytes) >= 4
and struct.unpack("<I", stdout_bytes[:4])[0] == len(stdout_bytes) - 4
):
stdout_bytes = stdout_bytes[4:]

error_msg = "Command '{}' returned non-zero exit status {}.\nStdout: {}\nStderr: {}".format(
cmd,
process_result.returncode,
stdout_bytes.decode(errors="replace").strip(),
process_result.stderr.decode(errors="replace").strip(),
)

raise exceptions.GoogleAuthError(error_msg)

# Check length of response
response_len_le = process_result.stdout[:4]
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21 changes: 21 additions & 0 deletions packages/google-auth/tests/oauth2/test_webauthn_handler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@ def test_malformated_get_assertion_response(os_get_stub, subprocess_run_stub):
response_len = struct.pack("<I", 5)
response = "1234567890"
mock_response = mock.Mock()
mock_response.returncode = 0
mock_response.stdout = response_len + response.encode()
subprocess_run_stub.return_value = mock_response

Expand All @@ -68,6 +69,7 @@ def test_failure_get_assertion(os_get_stub, subprocess_run_stub):

# process returns get response in json
mock_response = mock.Mock()
mock_response.returncode = 0
mock_response.stdout = response_len + response_json
subprocess_run_stub.return_value = mock_response

Expand Down Expand Up @@ -96,6 +98,7 @@ def test_success_get_assertion(os_get_stub, subprocess_run_stub):

# process returns get response in json
mock_response = mock.Mock()
mock_response.returncode = 0
mock_response.stdout = valid_plugin_response_len + valid_plugin_response_json
subprocess_run_stub.return_value = mock_response

Expand Down Expand Up @@ -146,3 +149,21 @@ def test_success_get_assertion(os_get_stub, subprocess_run_stub):
assert (
got_response.response.user_handle == success_response["response"]["userHandle"]
)


def test_plugin_nonzero_exit(os_get_stub, subprocess_run_stub):
response_json = b"detailed_gnubby_internal_crash_log"
response_len = struct.pack("<I", len(response_json))

mock_response = mock.Mock()
mock_response.returncode = 1
mock_response.stdout = response_len + response_json
mock_response.stderr = b"stderr dump"
subprocess_run_stub.return_value = mock_response

test_handler = webauthn_handler.PluginHandler()
with pytest.raises(exceptions.GoogleAuthError) as excinfo:
test_handler.get(GET_ASSERTION_REQUEST)

assert "returned non-zero exit status 1" in str(excinfo.value)
assert "detailed_gnubby_internal_crash_log" in str(excinfo.value)
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